bitbake.conf: Set AUTOREV to have a vardepvalue

bitbake.conf: Set AUTOREV to have a vardepvalue

If you have a recipe which does not include SRCPV in PV but does set
SRCREV = "${AUTOREV}" and you run do_fetch, then change the repo to a
new commit then run do_unpack, do_unpack will fail since the new commit
doesn't exist in the repo that was fetched.

The problem is the revision chosen is not represented in the do_fetch
task hash. It if were, the fetch would rerun first and the commit would be
present. It works when PV includes SRCPV since that does contain the chosen
commit from the AUTOREV.

The solution is to include the SRCPV value into the representation of AUTOREV
used for checksum calculation purposes.

Add a selftest for this issue.

(From OE-Core rev: 7b8ee9285a197784d51e339f1603240f49435846)

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