v4l-utils: test-media: add dmesg -n info before modprobes

Sometimes the modprobe vivid fails, but because dmesg is set to
the 'notice' level it is not clear why it fails since the usual
kernel info messages are filtered out.

Switch to dmesg -n info before each modprobe so we can actually
see what is going on.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>