bitbake: fetch2: Handle lockfiles for file:// urls redirected to mirrors

bitbake: fetch2: Handle lockfiles for file:// urls redirected to mirrors

We recently dropped lockfiles for file:// urls which in itself makes
sense.

If a file url redirects to something like an http:// mirror, we'd have
no lock taken for the original file and could race against others
trying to download the file. We therefore need to ensure there is a
lock taken in the mirror handling code.

This adds code to take such a lock, assuming it isn't the same lock
as the parent url.

(Bitbake rev: 913b6ce22cd50eac96e8937c5ffc704bfce2c023)

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