Add extend_volume for Huawei drivers

This patch adds extend_volume function for Huawei drivers.

Huawei T driver needs to create a slave LUN for the extended LUN.
And accordingly it needs to delete all these slave LUNs before deleting
the extended LUN.

HVS driver just sends a rest command to finish extending volume.

Change-Id: Iae17dba8c4d88ec09eb52b4a14bd17bc5a2c1ccc
Merge "Add extend_volume for Huawei drivers"