Separate FlashSystem FC and iSCSI common code

Separate FlashSystem FC and iSCSI common code

The patch is mainly to split original FC driver code into common
code and FC driver for IBM FlashSystem. iSCSI driver merged in L-1
has been inherited from original FC driver for common functions
already.

In this patch,
* Separate FC driver into new driver and common code.
* Modify iSCSI driver to inherite the common code.
* Common function _get_node_data in iSCSI driver is moved into
common code.
* Add locks in initialize_connection and terminate_connection
for iSCSI driver.
* Remove flashsystem_multipath_enabled to use Cinder iSCSI
multipath support.

Implements: blueprint ibm-flashsystem-split-fc
Change-Id: I166a14e3eef370a22f4c0a675d451a3a4a6989f1