<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
<check-sources.py> Set error/debug level to suppress all plugin messaging

Systems which lacked RHN registrations would repeatedly output the
"This system is not registered with..." message from the RHN
plugin. Setting the `YumBase` `preconf.errorlevel` and
`preconf.debuglevel` options to `-1` solves this by suppressing all
plugin-originating messaging.
Merge pull request #120 from dobbymoodge/check-sources-bugs

<check-sources.py> Set error/debug level to suppress all plugin messaging
<oo-admin-check-sources.py> Only display "re-run" message if problems detected

Added a state-tracking variable `problem` to
`OpenShiftAdminCheckSources` object so that the "Please re-run this
tool..." message can be displayed only when a problem is detected.
Merge pull request #121 from dobbymoodge/check-sources-bugs

<oo-admin-check-sources.py> Only display "re-run" message if problems detected