Fix unit tests: SKIP_ON_BOX_BASE_DIR_RESOLUTION

- recent pull request added a check (performed over ssh) to find the
  base-dir (e.g. resolve "~") on the box where brooklyn is installing
  software components. For unit-tests (e.g. run on buildhive) these
  can fail because the test machine does not have ssh keys set up.
  Therefore disable the base-fir resolution in all these unit tests.

- TODO: have a nicer way to disable them, without requiring this
  extra line in each unit test.
  Would it be a good start to have LocalhostMachineProvisioningLocation
  automatically skip this by default?