Work around python-nss bug on unrecognised OIDs
A bug in python-nss causes an error to be thrown when converting an
unrecognised OID to a string. If cert-request receives a PKCS #10
CSR with an unknown extension, the error is thrown.
Work around this error by first checking if the OID is recognised
and, if it is not, using a different method to obtain its string
representation.
Once the python-nss bug is fixed, this workaround should be
reverted. https://bugzilla.redhat.com/show_bug.cgi?id=1246729
Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>