devtool: upgrade: fetch remote repository before checking out new revision
If we're upgrading a recipe that fetches from git, and we've simply
fetched a tarball of the repo instead of directly from the upstream repo
(this can happen if you have PREMIRRORS set up as in poky with a core recipe,
e.g. kernelshark) then we won't have any new revisions, and the checkout
will fail with "fatal: reference is not a tree: <hash>". To avoid this,
do a "git fetch" before checking out the new revision.
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
