iotests/149: Remove qemu_img_pipe() call

iotests/149: Remove qemu_img_pipe() call

qemu_img_pipe calls blank their output when the command being run is a
'create' call and the command succeeds. Thus, the normative output for
this command in iotest 149 is to print a blank line. We can remove the
logging from this invocation and use a checked invocation, but we still
need to inspect the actual output to see if we want to retroactively
skip the test due to missing cipher support.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220321201618.903471-14-jsnow@redhat.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>