Implement Huawei SDSHypervisor connector

Huawei SDSHypervisor uses a private key-value data protocal,
so we add a new connector inherited from InitiatorConnector
and implement connect_volume and disconnect_volume.

The connector uses sds_cli cmd to implement attach/detach/querydev vol,
sds_cli will be put to a specific dir and the path is registered as a
system environment variable when sds is installed.

Change-Id: I4fa3306df982347afb5fb8e5d4d14612024b643a
Implements: blueprint huawei-sdshypervisor-driver
Merge "Implement Huawei SDSHypervisor connector"