nvmeof: Fix broken UTs
nvmeof: Fix broken UTs

This patch fixes broken nvmeof UTs. A few tests
called 'asert_called_once_with' method on mock object,
instead of calling 'assert_called_once_with'.
The mistake went undetected, because mock objects
were not configured to use auto-speccing.
To avoid the same problem in the future, configure all
mocks to use autospec.

Additionally, replace 'assert_not_called' method which
is not available on older versions of Python and caused
lower-constraints testenv to fail.

Change-Id: I54a91dfcfae774b1051662291afe1586e59901ac
Signed-off-by: Szczerbik, Przemyslaw <c8dbc5e4774c2434964b8a5117ce1fc85f0175e1@intel.com>

openstack/os-brick,openstack/os-brick