[OE-core] Only one copy of bitbake should be run against a build directory

[Phil Blundell]

Since updating my copy of bitbake to one which does this extra locking,
I've come to realise that the constraint of having only one copy of
bitbake running is a bit of a nuisance when making use of devshells.  I
used to quite often have one or two long-running devshells for packages
that I was actively working on, and then in parallel with that would use
bitbake to recompile other things.  With the new locking mechanism, as
soon as I have a single devshell open I am now prohibited from using
bitbake for anything else in that same build directory.

Would it be reasonable to exempt devshells from that locking or is there
some compelling reason why they need to be serialised?

thanks

p.