Bug 989765 - Fix output when old jboss not present in alternatives

https://bugzilla.redhat.com/show_bug.cgi?id=989765

alternatives --remove sends output to stderr if the requested
alternative to be removed doesn't exist.  Test for existence of
alternative before trying to remove it.

Also, if uninstall, cleanup the jbossas-7 alternative
Merge pull request #3220 from detiber/bz989765

Merged by openshift-bot