Collect packages when TestObserver#onHealthCheckFailed is called (2/n)

TestObserver#mHealthCheckFailedPackages is added to collect packages
when TestObserver#onHealthCheckFailed is called. It will be used to test
if resgistration/unregistration is done successfully.

TestController#mFailedPackages is also renamed to be distinguished from
mHealthCheckFailedPackages.

Bug: 140472424
Test: atest PackageWatchdogTest
Change-Id: I791e0a1b8e5d59ae766502b54a0782d509b209b5