releng: Provide a build property to skip automated UI tests

releng: Provide a build property to skip automated UI tests

Allow passing a `-Dskip-automated-ui-tests` option to skip running
the automated UI tests (like SWTBot and RCPTT modules) during
the Maven build.

Some setups may want to run these longer tests only in certain
conditions, or at a different frequency than the "normal" unit
tests.

Change-Id: Ifb1d6307d8bf4cddaba4e8835ea5d5e7595bbf80
Signed-off-by: Alexandre Montplaisir <alexmonthy@efficios.com>
Reviewed-on: https://git.eclipse.org/r/83403
Reviewed-by: Hudson CI
Reviewed-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Tested-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>