Resolve circular dependency when tracking dependencies.

When TRACK_DEPENDS=True, there is a circular dependency wherein virtualenv is
used to install virtualenv before a virtualenv has been established.
TRACK_DEPENDS does not work in any use case without this fix.

Change-Id: I7a6652ba091cb95dac3871b6c71edcd762a7be62
Closes-Bug: 1208867
Merge "Resolve circular dependency when tracking dependencies."