Disable chroot and add daemon-enable-jail flag

What does this MR do?

Disable chroot mechanism by default.

Adds the daemon-enable-jail flag which will allow users to enable the legacy chroot mechanism if anything goes wrong. This flag won't be available via Omnibus, instead users will need to define the environment variable and pass to Pages. For example, inside /etc/gitlab/gitlab.rb

gitlab_pages['env']['DAEMON_ENABLE_JAIL']="true"

TODO

• I added the Changelog (e.g. Changelog: feature) trailer to the commits that need to be included in the changelog
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines

Related to #589 (closed) and gitlab#331699 (comment 616236869)