restapi : Add Role with wrong permit id leads to 500 error(#908392)

Add Role with wrong permit id leads to internal server error.

This patch returns a proper error message when the permit id
is invalid.

Change-Id: I9adfda37e67d24f96933aa4eb8f79a8fdb416d62
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=908392
Signed-off-by: Ravi Nori <rnori@redhat.com>