The query processor global instance is going away. The schema_tables usage
of it requires a huge rework to push the qp reference to the needed places.
However, those places talk to system keyspace and are thus the users of the
"qctx" thing -- the query context for local internal requests.
To make cql tests not crash on null qctx pointer, its initialization should
come earlier (conforming to the main start sequence).
The qctx itself is a global pointer, which waits for its fix too, of course.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>