Teach charging job constraint tests about no-battery devices

In particular, don't prompt the tester about plugging/unplugging
on devices that do not have batteries, and don't bother running
the unplug-state tests even if they somehow get invoked directly.

Bug 34221968
Test: manual build of CtsVerifier & execution of the test
      with/without 'adb shell cmd battery set present 0' to
      mock hardwired-power for the DUT.

Change-Id: I5700dba3440daf23c6843084f6baf6a52ecd485c