Stabilize tst_qdbusabstractinterface and make it XFAIL

Stabilize tst_qdbusabstractinterface and make it XFAIL

This test was written incorrectly in a way which happened to allow it to
pass most of the time (but not all the time).

Reset the state of test objects between each test function, and mark the
broken functions with QEXPECT_FAIL and a link to a task.

Replace the unusual WaitForPinger construct with the usual
QTRY_VERIFY/QTRY_COMPARE method of verifying asynchronous operations.

Task-number: QTBUG-24262
Change-Id: I82d09002307c0b500bf60cd5b583674321b37609
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>