<oo-admin-check-sources> Bug 1023391 - repo priority and package conflicts checks are skipped when no role is specified or determinable

Updated `main()` method logic to exclude repo priority and package
conflicts checks when no role can be determined. Also guaranteed that
the `--role` option advice is emitted whenever the role can't be
determined.
Merge pull request #118 from dobbymoodge/check-sources-bugs

<oo-admin-check-sources> Bug 1023391 - repo priority and package conflicts checks are skipped when no role is specified or determinable