Set default TZ environment variable to avoid excessive stat calls

We should set the TZ environment variable of the system: https://blog.packagecloud.io/eng/2017/02/21/set-environment-variable-save-thousands-of-system-calls/

I noticed on GitLab servers, system calls to stat("/etc/localtime") flood the straces of unicorn workers:

63845 07:19:21.898343 c {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000138>
63845 07:19:21.898642 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000054>
63845 07:19:21.898797 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000043>
63845 07:19:21.899764 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000050>
63845 07:19:21.899965 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000045>
63845 07:19:21.900112 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000044>
63845 07:19:21.903702 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000059>
63845 07:19:21.904093 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000047>
63845 07:19:21.904463 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000056>
63845 07:19:21.905038 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000049>
63845 07:19:21.905344 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000046>
63845 07:19:21.905649 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000049>
63845 07:19:21.905936 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000163>
63845 07:19:21.906250 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000048>
63845 07:19:21.906413 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000046>
63845 07:19:21.906793 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000046>
63845 07:19:21.907259 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000047>
63845 07:19:21.907468 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000046>
63845 07:19:21.907619 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000044>
63845 07:19:21.907975 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000046>
63845 07:19:21.908437 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000047>
63845 07:19:21.908733 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000046>
63845 07:19:21.912262 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000061>
63845 07:19:21.912688 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000051>
63845 07:19:21.913042 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000050>
63845 07:19:21.913236 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000049>
63845 07:19:21.913390 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000048>
63845 07:19:21.913875 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000052>
63845 07:19:21.914129 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000050>
63845 07:19:21.914484 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000050>
63845 07:19:21.914999 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000053>
63845 07:19:21.915313 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000057>
63845 07:19:21.915629 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000058>
63845 07:19:21.916007 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000052>
63845 07:19:21.916170 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000048>
63845 07:19:21.916486 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000050>
63845 07:19:21.916865 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000054>
63845 07:19:21.917162 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000049>
63845 07:19:21.920820 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000062>
63845 07:19:21.921290 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000102>
63845 07:19:21.921621 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000057>
63845 07:19:21.921981 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000193>
63845 07:19:21.922410 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000211>
63845 07:19:21.922754 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000076>
63845 07:19:21.923159 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000051>
63845 07:19:21.923360 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=127, ...}) = 0 <0.000049>

I considered putting this in the omnibus-gitlab tracker because we could just set the Rails environment variable, but this seems like a system-wide setting.

/cc: @richardc, @WarheadsSE

Edited May 18, 2018 by Stan Hu