defining standard build targets in layer metadata

Hello all,

working on bitbake-setup made me consider that a true end-to-end
configuration tool should also know what to build, not only what to
set up.

Earlier bitbake-setup prototypes allowed defining "oe-targets":[...]
in its configuration files, but I later on realized this doesn't scale
and isn't flexible enough, and isn't in the right place to begin with.
So I took it out in the latest patchset.

So here's a quick, not-well-thought-out idea:

BB_TARGETS = "build:'core-image-minimal' test:'-c testmage core-image-minimal' "

defined somewhere in a layer (e.g. conf/distro/poky.conf or in a fragment).

And then one would be able to run

bitbake build
bitbake test
bitbake flash
bitbake deploy
etc.

which would standardize not only setting up a build but also running
it. The particular set of generic target names and their values could
be defined differently, but the basic idea would be similar.

Thoughts?

Alex