Fix Morph failing to update some cached git repos

I was getting the following error when running the 'do-release.py'
script:

    ERROR:root:Command failed: morph --quiet --trove-host=git.baserock.org list-artifacts baserock:baserock/definitions sam/auto-release minimal-system-x86_32-generic
    ERROR: Ref d67a0e110187abd560a1de63fa172894a52839d5 is an invalid reference for repo git://git.baserock.org/delta/linux

The commit that it wants did actually exist in git.baserock.org and the
logs show that Morph hadn't done a `git remote update` to get the commit
locally.

This turned out to be because it'd had already looked up a different ref
in linux.git. It hadn't needed to run 'git remote update', but it *had*
added linux.git to a "don't need to update this repo again" list. Oops!

I've moved the code in question to the cachedrepo module so that the repo
object keeps that of whether it should be updated. The bug is now fixed.

As a side effect this patch fixes the spurious 'Updating repo
file:///...' messages, which were printed even though repos with
file:/// URLs are never updated.

0 files changed, 0 insertions, 0 deletions