Remove deprecated LVM ISCSI and ISER Drivers

Remove deprecated LVM ISCSI and ISER Drivers

The LVMISCSIDriver and LVMISERDrivers were deprecated in the Kilo
release. This removes both drivers and related test code.

Any existing users of LVMDriver should switch to using the
LVMVolumeDriver and set the iscsi_helper to the desire iSCSI helper
(tgtadm, lioadm, or iseradm).

Some unit tests under these driver test classes were not actually
specific to these drivers. Relevant unit tests were moved to a
different test class if they looked useful.

Change-Id: I30aec59e639cdbbb50daa2caacc243518e593418