fix relative root access without the trailing '/' character

if GITLAB_RELATIVE_URL_ROOT was configured (e.g. /gitlab), the application
was not accessible at http://git.local.host/gitlab. The trailing '/'
character was required.

This commit fixes the issue.
fix nginx static route handling when GITLAB_RELATIVE_URL_ROOT is used.

nginx was not configured correctly to handle static routes due to
which user uploaded files (in issues/wiki/avatar) were not being
displayed.

This issue was particularly visible when gitlab was configured to
use a relative url root.

This commit fixes the issue.
clean up GITLAB_RELATIVE_URL_ROOT code
group nginx vhost config and relative root config codeblocks together