Fix bugs for Huawei driver

This fixes two bugs for Huawei iscsi driver.
(1)If firstly we map LUN 1(just not LUN 0) to host,we can also
find LUN 0 mapped,whose device path is '-'.Then we will failed
to map a real LUN 0.So,we avoid mapping LUN 0 to host by setting
every volume's host LUN ID larger than 0,instead of generating it
automatically.
(2)Check valid size of resource pools when creating snapshot and
make sure it larger than 1 GB.

Fixes bug: 1135618
Fixes bug: 1136980
Change-Id: I412e78bf84c95cb51431c45cc084e9ec6a8efb78
Merge "Fix bugs for Huawei driver"