Keep long-running MyRocks mtr tests in their own suite

[mdcallag]

I assume there isn't a MyRocks suite that has good coverage but doesn't have the long running tests.

When run like this ...

./mysql-test-run.pl --async-client --parallel=$dop --fast --mem \
        --max-test-fail=1000 --retry=0 --force --mysqld=--rocksdb \
        --mysqld=--default-storage-engine=rocksdb \
        --testcase-timeout=120 --suite-timeout=1800 \
        --mysqld=--default-tmp-storage-engine=MyISAM --suite=rocksdb

Running mtr for the "rocksdb" suite with --mem and a few tests timeout after 120 minutes. And there are many other tests that take between 100 and 4800 seconds. The slowest N in seconds are:

104     rocksdb.ttl_primary
104     rocksdb.ttl_primary
107     rocksdb.blind_delete_rr
108     rocksdb.blind_delete_rc
108     rocksdb.blind_delete_rr
109     rocksdb.blind_delete_rc
113     rocksdb.drop_table
114     rocksdb.drop_table
116     rocksdb.autoinc_crash_safe_partition
117     rocksdb.autoinc_crash_safe
117     rocksdb.autoinc_crash_safe
117     rocksdb.autoinc_crash_safe_partition
127     rocksdb.init_failure
129     rocksdb.init_failure
133     rocksdb.bloomfilter_skip
133     rocksdb.statistics
133     rocksdb.statistics
134     rocksdb.bloomfilter_skip
135     rocksdb.bloomfilter
135     rocksdb.bloomfilter
137     rocksdb.ttl_secondary
138     rocksdb.ttl_secondary
148     rocksdb.rocksdb_read_free_rpl
150     rocksdb.rocksdb_read_free_rpl
155     rocksdb.cardinality
157     rocksdb.drop_table2
162     rocksdb.cardinality
179     rocksdb.rocksdb_read_free_rpl_stress
181     rocksdb.rocksdb_read_free_rpl_stress
201     rocksdb.bulk_load_rev_cf
201     rocksdb.bulk_load_rev_data
203     rocksdb.bulk_load_rev_cf_and_data
203     rocksdb.bulk_load_rev_cf_and_data
203     rocksdb.bulk_load_rev_data
205     rocksdb.bulk_load_rev_cf
208     rocksdb.bulk_load
210     rocksdb.bulk_load
214     rocksdb.drop_table2
265     rocksdb.locking_issues
283     rocksdb.locking_issues
684     rocksdb.add_index_inplace_sstfilewriter
684     rocksdb.add_index_inplace_sstfilewriter
842     rocksdb.bulk_load_unsorted
846     rocksdb.bulk_load_unsorted_rev
851     rocksdb.bulk_load_unsorted
851     rocksdb.bulk_load_unsorted_rev
853     rocksdb.rqg_runtime
4520    rocksdb.rqg_transactions
4812    rocksdb.rqg_transactions