A support for system-level (or user-level) JGit configuration was
suboptimal. Gerrit admins had to use either $HOME/.gitconfig of the user
owning Gerrit process or a system-wide location for global JGit
configuration for all repositories served by a Gerrit site.
Replace the system-wide and user-global JGit configuration to be read from
$SITE/etc/jgit.config.
Change-Id: I5e60e2d4d686b605673fe14665479c3f8cc2a1e2
d34dfe399d