Remove RM pool configuration and yarn_pool query option/profile property

Admission control adds support for configuring pools via a fair scheduler
allocation configuration, so the pool configuration mechanism is no longer
needed. This also renames the "yarn_pool" query option to the more general
"request_pool" as it can also be used to configure the admission controller
when RM/Yarn is not used. Similarly, the query profile shows the pool as
"Request Pool" rather than "Yarn Pool".

Change-Id: Id2cefb77ccec000e8df954532399d27eb18a2309
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1668
Reviewed-by: Matthew Jacobs <mj@cloudera.com>
Tested-by: Matthew Jacobs <mj@cloudera.com>
Tested-by: jenkins