Allow host config to be overriden in backend

This allows you to specify host=XXX in your backend configuration
to override the host value that is specified in the DEFAULT section,
allowing for some backends to share a hostname while others can
have unique names.

Change-Id: Ie8894a7cebf350dc2d50567058a765482b9d97d7
Closes-bug: #1322366
Fix ISER scan retry option

The 'num_iscsi_scan_tries' option was renamed to
'num_volume_device_scan_tries'.

Remove it from the test where the deprecated name is
referenced since it is not used there anyway.

Fix the ISER driver to set the new config field rather than the
old one.  Presumably this made the num_iser_scan_tries option
not work since only the new field is passed to the brick
connector.

Closes-Bug: #1323741

Change-Id: I13ac4cce10894b541054fbda719bbc5fd555e3c1
Merge "Fix ISER scan retry option"
Merge "Allow host config to be overriden in backend"