Avoid Rebuilding Core and VMTest Descriptions

Only generate the core test and vmtest descriptions when something has
actually changed rather than everytime CTS is built. This should make
iterative test development in CTS more pleasant.

The rule targets are changed to be the paths of the test description
XML files in a separate directory outside of the CTS distribution.
The buildCts.py rule copies these XMLs when they change to the
final CTS distribution location and creates the final plan file.

The dependencies have also been changed to reply upon the full
package paths rather than their phony targets to avoid rebuilding
everything all the time.

Finally, the AppSecurity rule was removed, because I have taken
care of that in my prior change to the Makefiles in the CTS
project.

Change-Id: I88b92c7a4cb4c2c2e20f06641e7ba0604d37f805