Build and install the list of preqreqs by ABI.

Fix a bug where a test could be invoked with the incorrect prereqs.

Instead:
-prereqs are installed (and overwritten if needed) before
every test package invocation.
-as long as the abi doesn't change between test package invocations,
prereqs are not re-installed
-prereqs are only uninstalled after all tests are finished

bug:18176495
Change-Id: Ie19f6294d10b0c3484ef403c19f049eb71b6f050