Split extra IU searching into a separate script

Since some platform tests have been made Tycho-friendly, they also
need to be checked for extra requirements specified in the pom.

Such additional requirements are installed by the p2 director
before the test is run.

Also avoid duplicating the code that generates aggregated test
reports.

Change-Id: Icf38a9604d3134c088908fb53d8f4da8cbbf7b89
Signed-off-by: Mat Booth <mat.booth@redhat.com>
Reviewed-on: https://git.eclipse.org/r/94481