pom.xml cleanup

removed unnecessary (and harmful) useUIThread=true

reconsiled test timeout configuration and increated it from 600
to 900 seconds because tests are running for over 500 seconds
on slover vms already.

Signed-off-by: Igor Fedorenko <igor@ifedorenko.com>
replaced IWorkbench getWorkbenchWindows()[0] with getActiveWorkbenchWindow()

Although not documented, getActiveWorkbenchWindow() performs initialization of
the active workbench window if it hasn't been insitialized already.
getWorkbenchWindows() does not perform active window initialization and returns
empty array if none of the active windows has been intialized already.

The difference in behaviour does not cause any problems when tests run with
full UI, where window initialization happens on SWT.FocusIn event. I think.
At least this is what I saw on X11, not sure about other platforms. On headless
X servers, like vnc or xvfb SWT.FocusIn event does not appear to be sent and
getWorkbenchWindows returns empty array until some other code triggers
window initialization.

This results in intermittent test failures during automated Hudson builds,
dependending on which tests run first, calls to getWorkbenchWindows either
happen after workbench window initialization (tests succeed) or before
(test fail).

Signed-off-by: Igor Fedorenko <igor@ifedorenko.com>