Handled when Try is Closed

CompletedProcess(args=['./mach', 'try', 'auto', '--push-to-vcs'], returncode=1, stdout=b'Creating temporary commit for remote...\nA try_task_config.json\npushing to ssh://hg.mozilla.org/try\nsearching for changes\nremote: adding changesets\nremote: adding manifests\nremote: adding file changes\nremote: \nremote: \nremote: ************************** ERROR ****************************\nremote: try is CLOSED! Reason: Windows OOM\nremote: To push despite the closed tree, include "CLOSED TREE" in your push comment\nremote: *************************************************************\nremote: \nremote: \nremote: transaction abort!\nremote: rollback completed\ntemporary commit removed, repository restored\nError running mach:\n\n    mach try auto --push-to-vcs\n\nThe error occurred in code that was called by the mach command. This is either\na bug in the called code itself or in the way that mach is calling it.\nYou can invoke ``./mach busted`` to check if this issue is already on file. If it\nisn\'t, please use ``./mach busted file try`` to report it. If ``./mach busted`` is\nmisbehaving, you can also inspect the dependencies of bug 1543241.\n\nIf filing a bug, please include the full output of mach, including this error\nmessage.\n\nThe details of the failure are as follows:\n\nsubprocess.CalledProcessError: Command \'(\'/usr/bin/hg\', \'push-to-try\', \'-m\', \'Tasks automatically selected.\\n\\nmach try command: `./mach try auto --push-to-vcs`\\n\\nPushed via `mach try auto`\')\' returned non-zero exit status 255.\n\n  File "/builds/worker/checkouts/gecko/tools/tryselect/mach_commands.py", line 366, in try_auto\n    return run(command_context, **kwargs)\n           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File "/builds/worker/checkouts/gecko/tools/tryselect/mach_commands.py", line 173, in run\n    return mod.run(**kwargs)\n           ^^^^^^^^^^^^^^^^^\n  File "/builds/worker/checkouts/gecko/tools/tryselect/selectors/auto.py", line 108, in run\n    return push_to_try(\n           ^^^^^^^^^^^^\n  File "/builds/worker/che...

The easy fix is to just not error and leave a comment saying we couldn't submit to try because it was closed. The harder fix is to change the state machine so it tries submitting to try at a later time. That change might be made even larger to handle various external services being down (Bugzilla, Try, Treeherder...)

Start with tools/tryselect/mach_commands.py at try_auto, then follow the stack trace through selectors/auto.py and push_to_try. Reproduce the closed-Try response and define completion as handling that response without an unhandled command error, while preserving the reported outcome to the user.