Before commit e0346c1, a non-system repo could specify
remotes-config-dir and have remotes read from there. However, adding
remotes would only be done in the config dir for a system repo. Restore
that by respecting remotes-config-dir when no sysroot is found and
adding back the ostree_repo_is_system() check when adding remotes.
Closes: #1133Closes: #1151
Approved by: cgwalters
Dan Nicholson