Fix the jobs flag to not break with older bundler

Systems using bundler version 1.4 or earlier do not have the -j flag availabe
for the bundle command.  To prevent this, we need to default the -j flag to not
be present and only enable it if the user explicitly declares
gitlab_bundler_jobs.
install: Fix spec tests (syntax lint warning)
Merge branch 'atomaka-atomaka/bugfix/jobs-default'