engine: Set proper severity to a failed command

The audit log of commit networks changes failure
should be changed to error to reflect its true
nature.

Change-Id: Ib7254bc1506d57edc158d034c7d06fe6e1e9c5c7
Bug-Url: https://bugzilla.redhat.com/1061727
Signed-off-by: Moti Asayag <masayag@redhat.com>