Add QSqlDatabase::moveToThread() to be able to move the driver instance
to another thread.
[ChangeLog][Sql][QSqLDatabase] QSqlDatabase gained two new functions
moveToThread() and currentThread() to be able to use it in another
thread than the one it was created in.
Fixes: QTBUG-39957
Change-Id: I9cb51358f73a3a2fa72813bfdbe059279d388bd7
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>