Bug#49369: No testcase for key caches on partitions

The original test case was lost when
merging WL#4571.

Added the testcase.

mysql-test/include/check_key_reads.inc

+# include file for checking if variable key_reads is zero
+let $key_reads= query_get_value(SHOW STATUS LIKE 'key_reads',Value,1);
+--disable_query_log
+eval SELECT IF($key_reads = 0, "Yes!", "No!") as 'Zero key reads?';
+FLUSH STATUS;
+--enable_query_log

mysql-test/include/check_key_req.inc

+# include file for checking if variable key_reads = key_read_requests
+let $key_reads= query_get_value(SHOW STATUS LIKE 'key_reads',Value,1);
+let $key_r_req= query_get_value(SHOW STATUS LIKE 'key_read_requests',Value,1);
+let $key_writes= query_get_value(SHOW STATUS LIKE 'key_writes',Value,1);
+let $key_w_req= query_get_value(SHOW STATUS LIKE 'key_write_requests',Value,1);
+--disable_query_log
+eval SELECT IF($key_reads = $key_r_req, "reads == requests", "reads != requests") as 'reads vs requests';
+eval SELECT IF($key_writes = $key_w_req, "writes == requests", "writes != requests") as 'writes vs requests';
+--enable_query_log