TESTS: change modeselect to become /dev/sg-aware

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
TESTS: Flag a whole bunch of tests as not supported on non-iSCSI backends

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
TESTS: Allow inquiry data to contain padding IFF it is all zero

Some implementations may send oversized data coming back from Inquiry.
Warn about this instead of failing the test but then perform additional
checks that the padding MUST be zero or else fail the test.

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>