Update EMC SMI-S Driver

Update EMC SMI-S Driver

1. Merged with Avishay's changes(https://review.openstack.org/#/c/
19808/3) and removed copy volume<->image from my driver.
2. Also did some refactoring based on Mike's comments
last time (See https://review.openstack.org/#/c/19979/).
Made the following changes in emc_smis_common:
- Added a member variable conn to save get_ecom_connection
and moved exceptions inside the helper function get_ecom_connection.
- Also moved exceptions inside find_pool and get_storage_type.
- Added test cases so get_ecom_connection, find_pool, and
get_storage_type will be covered.
3. Made changes in emc_smis_common to handle both iscsi and fc.

Change-Id: I56db3ba41215489f6afe840ce5310a31f28bf5ae