bitbake: Add start of bitbake regression/self testing

bitbake: Add start of bitbake regression/self testing

This adds some basic unit testing for the codeparser and data store code. Many of
the actual test cases were taken from work by Chris Larson's OE-Signatures work but with
changes to adapt to the current bitbake APIs we need to test.

I also imported CoW tests written by Holger Freyther from the original bitbake-test
codebase: http://svn.berlios.de/wsvn/bitbake/trunk/bitbake-tests/tests/ and
some tests from the doctests that were removed in commit:
http://git.openembedded.org/bitbake/commit?id=3a11c2807972bbbddffde2fa67fc380d159da467

(Bitbake rev: ae4a95780e3e08cf73c854efa8cd93379e00c4e5)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>