engine:  Attach/Detach two (or more) nets with labels to cluster fails

When more than one network with a label are attached/detached to/from a
cluster via multiple action- Attach/DetachNetworkToVdsGroup an internal
command Attach/DetachNetworksFromCluster is called.
Due to changes in internal commands protocol- commands that are called
internally should have two ctors-
1. Ctor(T parameters)
2. Ctor(T parameters, CommandContext cmdContext)
Since the Attach/DetachNetworkToVdsGroup didn't have the first ctor there
was an exception.

Change-Id: I8862de722b42360d215285e3bd29708cc5ceec68
Bug-Url: https://bugzilla.redhat.com/1124392
Signed-off-by: Alona Kaplan <alkaplan@redhat.com>