rgmanager: Fix orainstance.sh error checking

Pull in the fixed error checking that was added to RHEL6 oracledb.sh
to fix rhbz#471066

Resolves rhbz#723819

Acked-by: Fabio M. Di Nitto <fdinitto@redhat.com>
Signed-off-by: Ryan McCabe <rmccabe@redhat.com>