In another test run the test failed to continue because the webdriver could not be powered off after successfully running a spec for a batch of Aps.

Traceback (most recent call last):
  File "/usr/local/autotest/server/server_job.py", line 690, in run
    self._execute_code(server_control_file, namespace)
  File "/usr/local/autotest/server/server_job.py", line 1187, in _execute_code
    execfile(code_file, namespace, namespace)
  File "/usr/local/autotest/results/69041135-chromeos-test/chromeos3-row1-rack2-host4/control.srv", line 39, in <module>
    parallel_simple(run_chaos_wpa2psk, machines)
  File "/usr/local/autotest/server/subcommand.py", line 93, in parallel_simple
    function(arg)
  File "/usr/local/autotest/results/69041135-chromeos-test/chromeos3-row1-rack2-host4/control.srv", line 36, in run_chaos_wpa2psk
    runner.run(job)
  File "/usr/local/autotest/server/cros/chaos_lib/chaos_runner.py", line 242, in run
    utils.power_off_VM(webdriver_master, webdriver_instance)
  File "/usr/local/autotest/server/cros/network/chaos_clique_utils.py", line 83, in power_off_VM
    master.run(power_off_cmd)
  File "/usr/local/autotest/server/hosts/ssh_host.py", line 190, in run
    options, stdin, args, ignore_timeout)
  File "/usr/local/autotest/server/hosts/ssh_host.py", line 157, in _run
    raise error.AutoservRunError("command execution error", result)

AutoservRunError: command execution error
stderr:
VBoxManage: error: Invalid machine state: PoweredOff
* Command:
    /usr/bin/ssh -a -x  -o ControlPath=/tmp/_autotmp_qoEfU7ssh-master/socket
    -o StrictHostKeyChecking=no -o UserKnownHostsFile=/tmp/tmpXzPE2b -o
    BatchMode=yes -o ConnectTimeout=30 -o ServerAliveInterval=300 -l
    chaosvmmaster -p 22 chromeos3-chaosvmmaster.cros.corp.google.com " if type
    \"logger\" > /dev/null 2>&1; then logger -tag \"autotest\"
    \"server[stack::run_chaos_wpa2psk|run|power_off_VM] -> ssh_run(VBoxManage
    controlvm chromeos3-chaosvm4 poweroff)\";fi; VBoxManage controlvm
    chromeos3-chaosvm4 poweroff"
Exit status: 1
Duration: 0.21581697464

stderr:
VBoxManage: error: Invalid machine state: PoweredOff (must be Running, Paused or Stuck)
VBoxManage: error: Details: code VBOX_E_INVALID_VM_STATE (0x80bb0002), component Console, interface IConsole, callee nsISupports
VBoxManage: error: Context: "PowerDown(progress.asOutParam())" at line 222 of file VBoxManageControlVM.cpp


If the vm is powered off why do we attempt to power it off again? In the code, i see that we do unconditional power on/off. It looks like this may lead to issues when we perform operation on invalid states of the vm. Would be better to get the current state of a before running power on/off.