Reset System properities between tests

This is to avoid test leakage.

The properties are reset to their initial values with this
change, clearing any of the ones set by tests. Vogar
was already doing something like this.

Some of the existing property setting was rendered
unnecessary / pointless by Narayan's immutable
system property commit
(f63153ac0ec510b0111d01805097bbd08ccf64ab).

Note: This change will cause a merge conflict for the
internal master due to changes in the CTS runner.

Change-Id: I7edfc325857f701ab0c5b9958703b3a592e8eb82