bitbake: fetch/git: Handle github dropping git:// support

github is dropping support for git protocol in Git urls. Add code to remap
this to https in a way that could be used in older bitbake versions.

(Bitbake rev: af479e239d1e4dc93f0162c5936369a94c1c529d)

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