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This change modifies ArcVmClientAdapter to start ARCVM before
login (to implement mini-ARC). Among the changes are:
 - Starts mini-ARCVM with a generic user kArcVmDefaultOwner
 - Sets correct owner id during UpgradeArc()
 - Stops VM if UpgradeArc() fails
 - On StopArcInstance(), checks if mini-ARC or full ARC is running
 - Update unittests

BUG=b:144542975
TEST=ArcVmClientAdapterTest unittests
TEST=tast run <DUT> arc.Boot.vm crostini.Basic.buster_amd64_stable
TEST=build and flash. On login screen, check chrome log and syslog
to make sure ARCVM has started successfully. Check guest logcat and
make sure init is blocked on arcvm-boot-notification-client. After
login, check that instance is upgraded successfully and Play Store
is able to start.

Change-Id: I190a9ede041b53f0dbcb1773ea82b2e0ac51ae54
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2354623Reviewed-by: Ryo Hashimoto <hashimoto@chromium.org>
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Commit-Queue: Willie Koomson <wvk@google.com>
Cr-Commit-Position: refs/heads/master@{#840674}