engine: Fix few eclipse warning

The AuditLogableBase doesn't implement Serializable, therefore
it doesn't required any serial id.

The serial warning can be removed from CommandBase as well.

Clear the type from CommandBase.validate() signature which hides
the T type defined as a parameter class type on the class signature.

Change-Id: I4c6e80252f0a9d907488be6ede45271c936f5de6
Signed-off-by: Moti Asayag <masayag@redhat.com>