udev-extraconf: allow mount.blacklist to be inhibited
udev-extraconf: allow mount.blacklist to be inhibited

It is useful to test mount.sh by providing a filesystem image that is
bound to a loopback device via `losetup`. But this is normally
prevented (for fairly good reasons, I'd imagine) due to /dev/loop being
present in /etc/udev/mount.blacklist.

And as an expedient for this use case, skip the mount.blacklist checks
if the environment variable DISABLE_AUTOMOUNT_BLACKLIST is nonempty.

Natinst-Rally-ID: TA51600
Natinst-Reviewboard-ID: 62546
Natinst-CAR-ID: 452621
Signed-off-by: Richard Tollerton <67c688e7f7482ba5c4ebe3d70bc77594748182a6@ni.com>

ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt