bitbake: fetch2: Sanity check SRCREV matches rev/tag parameter

bitbake: fetch2: Sanity check SRCREV matches rev/tag parameter

Add a sanity check so that if some SRCREV is set and a rev parameter is given
to the url, the revision given should match.

Any tag parameter behaves the same as rev. If both are specified, error to
tell the user we're confused rather than do something which may or may not
be what they intended.

Also add some unittests for this.

(Bitbake rev: e82a4ab48991035866da9914c8b75a9bfbc9a7fc)

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