Add Scalable Pool Configuration to Admission Controller.

Add configuration parameters to Admission Controller that scale with
the number of hosts in the resource pool. The planned parameters are

• Max Running Queries Multiple - the Multiple of the current total number of running Impalads which gives the maximum number of concurrently running queries in this pool.
• Max Queued Queries Multiple - the Multiple of the current total number of running Impalads which gives the maximum number of queries that can be queued in this pool.
• Max Memory Multiple - the Multiple of the current total number of running Impalads which gives the maximum memory available across the cluster for the pool.