Fix bugs for Huawei driver

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