cerbero: Fix recipe status reset for git repositories

Submitted by Robert Swain

Link to original bug (#747514)

Description

Tests show that cerbero seems to reset the status of a recipe based, partially, upon what is fetched from a git repository rather than the HEAD commit hash.

This means that recipe build states get reset unnecessarily when the recipe points to a specific commit and the branch to which that commit belongs is updated. It also means that recipe build states are not updated if the specific commit pointed to is changed within that which is fetched.

Also, I changed the commit hash pointed to by a recipe and I expected that changing the recipe would trigger a rebuild (after running fetch-package --reset-rdeps --full-reset <package>) but it did not. It had even changed the commit that was checked out.