crosperf: remove dead machine in the runtime.

This checks whether a machine is reacheable after a test run.
If the machine is dead, we remove it from the machine list in the
machine manager.

BUG=None
TEST=crosperf a simple case passes.

Change-Id: Ie40a4a41715f2dc0349666079faa599b3c8aa667
Reviewed-on: https://gerrit-int.chromium.org/38578
Reviewed-by: Luis Lozano <llozano@chromium.org>
Commit-Queue: Yunlian Jiang <yunlian@google.com>
Tested-by: Yunlian Jiang <yunlian@google.com>
2 files changed