tgt and iscsi code need some minor fixes.  Moved the settle call during
simple read testing.  In iscsi.py, generic_mkfs and generic_mount need
to be called from the main body of the task.  An extraneous iscsiadm
command was removed.  The tgt size is now not hard-coded.  It is extracted
from the property and defaults to 10240.

Fixes: #6782
Merge branch 'wip-fix-teuth-tgt-wusui'