Adjust max for memory settings
Adjust max for memory settings

- The new maximum strikes a balance between a realistic
  production memory setting and a low enough value that
  a slider is useable.
- Include a note in the setting description pointing out
  that custom values can be set by clicking on the
  pencil next to the setting.

prestodb/ambari-presto-service,TeradataCenterForHadoop/ambari-presto-service