engine: Improved host life cycle

The following patch is introducing a folloing improvements:
1. By adding HostStoragePoolParametersBase class, it is possible to pass
   vds and storage pool to command and no need to perform additional query at command
   Benefit, reduced two queries at ConnectHostToStoragePoolServersCommand and at
   DisconnectHostFromStoragePoolServersCommand
2. From now DisconnectHostFromStoragePoolServersCommand running with out openning transaction,
   no need , DB is not updated so no need for global transaction.
   Benefit - less long transaction during moving host to maintainance
3. Removed canDoAction of DisconnectHostFromStoragePoolServersCommand, usually will be true, reason
   it is useless.
   Benefit - less useless code, less useless checks

Change-Id: I14b07f4568a78e4da359c1ac3bfd8417550574d7
Signed-off-by: Michael Kublin <mkublin@redhat.com>