[DOCS] Genericize impala_config_performance page
[DOCS] Genericize impala_config_performance page

Reword one reference to 'CM' inside a comment.

Change-Id: I34509e677d220ecadd33e150143bacc6d7f302ae
Reviewed-on: http://gerrit.cloudera.org:8080/6385
Reviewed-by: Ambreen Kazi <e1177c5e2e2eee99dbd6ef5fbe233f66bddb1c06@cloudera.com>
Reviewed-by: John Russell <308573a947c636ab812b35943b6242633bef8113@cloudera.com>
Tested-by: Impala Public Jenkins

michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala