Adding support for consistency groups in huawei driver.
supports the following interfaces:
1.create_consistencygroup
2.delete_consistencygroup
3.update_consistencygroup
4.create_cgsnapshot
5.delete_cgsnapshot
DocImpact
Implements: blueprint support-huawei-consistency-group
Change-Id: Ib35c382d1cc008f483a60da557781435dde098e1
