MDEV-36666 - atomic.alter_table still times out often

According to buildbot cross-reference atomic.alter_table is failing ~10
times a day due to 900 seconds test case timeout. Split it into two
tests: atomic.alter_table_myisam and atomic.alter_table_innodb.
It should reduce failure frequency down to once a day or so, similarly
to atomic.alter_table_aria test.

Diabling InnoDB for MyISAM/Aria/RocksDB tests makes them 20-35% faster.

mysql-test/suite/atomic/README.txt

@@ -3,7 +3,7 @@ the following:
 
 - Add # before --exec echo "restart" ...
 - Force $e (engine), $c (crash point) and $r (crash position) to the values
-  where things goes wrong. See comments in alter_table.test for how to do this.
+  where things goes wrong. See comments in alter_table.inc for how to do this.
 - start mariadbd in a debugger
 
 run the following in the debugger

mysql-test/suite/atomic/alter_table.inc

@@ -1,6 +1,5 @@
 --source include/long_test.inc
 --source include/have_debug.inc
---source include/have_innodb.inc
 --source include/have_log_bin.inc
 --source include/not_valgrind.inc
 

mysql-test/suite/atomic/alter_table_aria.test

@@ -4,4 +4,4 @@
 let $engine_count=1;
 let $engines='aria';
 let $extra_engine=myisam;
---source alter_table.test
+--source alter_table.inc

mysql-test/suite/atomic/alter_table_innodb.test

@@ -0,0 +1,7 @@
+#
+# Test atomic alter table with InnoDB
+
+--source include/have_innodb.inc
+let $engine_count=1;
+let $engines='innodb';
+--source alter_table.inc

mysql-test/suite/atomic/alter_table_myisam.test

@@ -0,0 +1,6 @@
+#
+# Test atomic alter table with MyISAM
+
+let $engine_count=1;
+let $engines='myisam';
+--source alter_table.inc

mysql-test/suite/atomic/alter_table_rocksdb.test

@@ -3,4 +3,4 @@
 let $engine_count=1;
 let $engines='rocksdb';
 set global rocksdb_flush_log_at_trx_commit=1;
---source alter_table.test
+--source alter_table.inc

mysql-test/suite/atomic/alter_table_trigger.test

@@ -7,7 +7,7 @@
 #
 # Testing of atomic create table with crashes in a lot of different places
 #
-# This is very similar to the alter_table.test, but includes testing of
+# This is very similar to the alter_table.inc, but includes testing of
 # triggers in with ALTER TABLE .. RENAME.
 #