Add aggregate metric test scenario with buckets > 1

Be able to generate expected aggregate data to handle multiple buckets.  For example, 

raw data
 `[ {time1, data}, {time2, data}, {time3, data}, {time4, data}]`
test 
`get aggregate metric start=time1, end=time4, buckets=2`

expected result
`[{start:time1, end:time2, min, max, avg... of 1st and 2nd pair}, {start:time3, end:time4,  min, max of 3rd and 4th pair}]`
