oeqa/selftest: Add test for Yocto source mirror functionality/completeness
We've had a number of occasions where the Yocto Project source mirrors have not
been complete or functioning correctly. This adds a test so that if this happens
we find out out it sooner.
It also only works over http meaning we should be able to test that anyone behind
an http only proxy (no git protocol) also has functional fetches for OE-Core and
layers built by the core of the project.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
