support TRACE_FAILONLY env variable

In order to get similar behavior to the way testr out of the box
works, only displaying failing results, all the user to define
TRACE_FAILONLY environment variable (any value will do). After this
point only failures, and things leaking out of stderr will end up on
the screen.

We also need to remove the suppression of the inline fail dumps for
this to have the impact that you'd expect.

Change-Id: I72911adc8a03450522429c52db661ec0a1bc4678
VMware: Fix deletion of an instance with no files

When a managed object doesn't contain a property, RetrievePropertiesEx
doesn't return None; it doesn't return the property at all. We were
testing for this incorrectly and not handling it in the code.

Change-Id: I77a0ba4eb5a6cc6075db9c67294f30abaa0e474d
Merge "VMware: Fix deletion of an instance with no files"
Merge "support TRACE_FAILONLY env variable"