meta/lib/oe/recipeutils.py: handle fetcher errors when checking for new commits

meta/lib/oe/recipeutils.py: handle fetcher errors when checking for new commits

Recent freedesktop instabilities are causing 'devtool check-upgrade-status' to
fail with:

bb.fetch2.FetchError: Fetcher failure: Fetch command export PSEUDO_DISABLED=1; git -c gc.autoDetach=false -c core.pager=cat -c safe.bareRepository=all -c clone.defaultRemoteName=origin ls-remote https://gitlab.>
fatal: unable to access 'https://gitlab.freedesktop.org/mesa/kmscube/': The requested URL returned error: 502

and not print any results for this one or any unrelated recipes included in the check.

This change handles the error, so that if some upstream server isn't working
properly, latest upstream revision for that is marked as unknown, a
warning is printed and upstream version check for other recipes
isn't thwarted:

WARNING: Unable to obtain latest revision: Fetcher failure: Fetch command export PSEUDO_DISABLED=1; git -c gc.autoDetach=false -c core.pager=cat -c safe.bareRepository=all -c clone.defaultRemoteName=origin ls-remote https://gitlab.freedesktop.org/mesa/piglit.git  failed with exit code 128, output:
remote: GitLab is not responding
fatal: unable to access 'https://gitlab.freedesktop.org/mesa/piglit.git/': The requested URL returned error: 502

piglit                    1.0             UNKNOWN_BROKEN  Ross Burton <ross.burton@arm.com>

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>