[libofono-qt] Use QMAKE_LFLAGS to make sure we link to the libofono-qt under test

This prevents us from accidentally linking against a system copy.

This won't protect us from running the tests against a system copy, for that we
need LD_LIBRARY_PATH or rpath, but this will at least result in successful and
proper builds.
[libofono-qt] Use TEMPLATE=aux

This doesn't build anything, it just installs an XML file.

qmake's default template is app, which assumes it's building a binary.
[libofono-qt] Don't use QT_INSTALL_PREFIX for testcases.

We want these to go into /opt/tests, QT_INSTALL_PREFIX will expand to /usr,
which would make for /usr/opt/tests.
[libofono-qt] Correct packaging of testcases.