[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