Add having clause.

you can query having clause like this.

   select mean(cpu), host from service group by time(1m), host having top(mean, 10) and host = 'service1'

Having Clause Syntax:

   group by columns [having CONDITIONS]

* having clause supports top and bottom. other aggregate function doesn't support.
  * you can't call top and bottom multiple times.
  e.g) having top(a, 10), bottom(b, 10) could not evaluate