CTDB: fix incorrect db corruption reports (bsc#1101668)

If a database was disconnected during an active transaction, then
tdbdump may fail with e.g.:

/usr/bin/tdbdump /var/lib/ctdb/persistent/secrets.tdb.1

Failed to open /var/lib/ctdb/persistent/secrets.tdb.1
tdb(/var/lib/ctdb/persistent/secrets.tdb.1): FATAL:
tdb_transaction_recover: attempt to recover read only database

This does *not* indicate corruption, only that tdbdump, which opens the
database readonly, isn't able to perform recovery.

Using tdbtool check, instead of tdbdump, passes:

tdbtool /var/lib/ctdb/persistent/secrets.tdb.1 check

tdb_transaction_recover: recovered 2146304 byte database
Database integrity is OK and has 2 records.

Drop the tdbdump checks, and instead rely on the core ctdb event script,
which performs the same checks with tdbtool.

Signed-off-by: David Disseldorp <ddiss@suse.de>