BUG-994: optimize resolveRelativeXPath()

This patch is a slight optimization of the method which takes advantage
of the fact that we do not need to return a List anymore.

Change-Id: I05ed7b96feca26247a6d73dfe2e758846155302f
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-994: optimize resolveRelativeXPath()"