[RFC] Respect force flag in runall and runonly

[Joshua Watt <jpewhacker@gmail.com>]

Implements the ability to run bitbake commands like:

 $ bitbake -f --runall fetch core-image-mimimal
 $ bitbake -f --runonly fetch core-image-minimal

which will invalidate the stamps for all affected tasks forcing them to
run even if they have already.

I've found this useful in a few circumstances. Most recently, I was
attempting to do A/B performance comparison of so package QA checks, so
it was pretty easy to figure out the impact of various QA checks with:

 $ time bitbake -f --runall package_qa core-image-minimal

Additionally, I currently do a number of actions like this (because we
don't have runall):

 $ bitbake -g <image>
 $ xargs -a pn-buildlist bitbake -f -c <action>

And I would like to replace them with

 $ bitbake -f --runall <action> <image>

Is this something that is even necessary/wanted?