filesystem settings for faster buildserver VMs

Normally, filesystems do a lot to ensure that cached writes are reliably written to disk. For a buildserver VM, this is not needed. Either the build is successful and the binary is exported out of the VM, or something fails and nothing more is needed. The buildlog is exported on the fly already. Then the whole thing is destroyed.

The filesystem should be tuned for best write performance. Here are some ideas:

• sed -i 's/rw,discard/rw,commit=100,discard/' /etc/fstab
• tune2fs -o journal_data_writeback /dev/vda1