ctdb-tests: Fix and extend read-only records test

ctdb-tests: Fix and extend read-only records test

This test currently counts the number of read-only-enabled databases
and expects there to only be 1.  It fails when there are existing
databases with read-only already enabled.  Instead, check just the
test database.

Clean up the test by adding some functions to check for precisely the
read-only flags that should be set on a node after each operation.

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>