Tinderbox chroot change mount to readonly on demand

[Chris Rees]

Hi all,

Done a couple of little changes to the mounting logic [1], as well as
modify requestMount to auto-add the -u flag to already mounted
filesystems, this will allow us to toggle the readonly flag.

It looks rather tricky to be playing with something as major as where
the build is called from, but I think I'm doing it properly...

Does anyone see any major errors in what I've done so far? Progress is
slow because I'm at work this week, and very busy writing pupil
reports as well :/

Chris

[1] http://www.bayofrum.net/~crees/patches/tinderbox-buildmount.patch