[tests] tests.xml: remove effectless pre-steps

Relates NEMO#664
[tests] tests.xml: fix test binary name

Relates NEMO#664
[tests] runstarget.sh: do not redirect output

Relates NEMO#664
[tests] runstarget.sh: do not always exit with 0

The test binary is now ``exec''ed to work well as GDB's exec-wrapper.

Relates NEMO#664
[tests] Fix test data files path

Relates NEMO#664
[tests] ClientWorkerTest: do not hang upon init()

Relates NEMO#664
[tests] Fix failures on opening database file

QSQLITE driver automatically creates database file only if the directory exists.

Relates NEMO#664
[tests] Fix after rename to buteosyncml

Relates NEMO#664
[SyncAgent] clean listen after single request

Regression introduced by 83a7c4fb196bd62083ac928ddf9dd91b2fc5f10b

Detected by SyncAgentTest::testSync(), SyncAgentTest.cpp:147

Relates NEMO#664
[tests] Use QSKIP() instead of QVERIFY(false)

Relates NEMO#664
[tests] Fix SessionHandlerTest init/cleanup

Failure to remove temporary DB file causes
SessionHandlerTest::testClientAuthMD5WithoutNonce3(),
SessionHandlerTest.cpp:1063 to fail on second (and following) test execution.

Introduced by d9234ca17b56a542c6df2179cd3d067e571a896f

Relates NEMO#664
[tests] Fix MockSyncItem key assignment

Detected by CommandHandlerTest::testSyncAdd(),
CommandHandlerTest.cpp:286

The test case has most probably started failing when ec17dfc introduced
calling newItem->setKey() inside StorageHandler::addItem().  Anyway,
according to the documentation of StoragePlugin::addItems(), the
implementation was wrong since the initial commit. Also see 7b8c432
(removing the aLocalKey argument -- probably wrong conflict resolution)
and c4ce210 (adding aLocalKey again).

Relates NEMO#664