<oo-admin-check-sources.py> Bug 1023361, fix reference to unassigned var

This commit places more find_package_conflicts logic in the try: block
so that the ose_pkgs list never gets referenced if the repoid being
checked doesn't match an enabled repo.

This also adds a check to prevent the rhel6 base repo from being
checked if it's not in the enabled repoids list
Merge pull request #113 from dobbymoodge/check-sources

<oo-admin-check-sources.py> Bug 1023361, fix reference to unassigned var
<oo-admin-check-sources.py> Bug 1023363, Fix typo

add /etc to rhnplugin.conf path
Merge pull request #114 from dobbymoodge/check-sources

<oo-admin-check-sources.py> Bug 1023363, Fix typo
<install> refactor rhsm+rhn conf; preflight checks

rhsm repo conf options outsourced to a function so maintenance requires
only changing the repo name in one place.
Same thing for "rhn" method; also made this idempotent so can rerun the
install without filling up the plugin conf.
Preflight checks now look for user/pass on rhn/rhsm (now consolidated
into common var names).
Also removed a minor preflight problem where rpm -V fails for no good
reason on a re-install; used plain rpm -q instead to test rpmdb.
Merge pull request #115 from sosiouxme/enterprise-2.0

<install> refactor rhsm+rhn conf; preflight checks