Teach "prepAllTestBundles.sh" to honour tycho surefire exclusions.

Previously, we would ignore any "<excludes>" specified in pom.xml
files. This had the effect of trying to run classes as test cases
that were never meant to be run that way. This would manifest as
a failure due to "no runnable methods" during a test suite run.

Change-Id: Iad649c1b8354134fadf4f74bea1a5035f2942f4a
Signed-off-by: Mat Booth <mat.booth@redhat.com>
Reviewed-on: https://git.eclipse.org/r/69968