Updates to groupByNodeMetric

After thinking about the results of groupByMultiNode, I'm not happy about how
the resulting series is named - it loses a bunch of information that
could be used in subseqent function calls.

Previously, the resulting series list was akin to:

    alias(asPercent(servers.server1.value1,servers.server1.total),'server1')
    alias(asPercent(servers.server1.value2,servers.server2.total),'server2')
    ...
    alias(asPercent(servers.serverN.value2,servers.serverN.total),'serverN')

Resulting in a seriesList of:

    server1, server2,...serverN

With this change, the results are now:

    servers.server1.asPercent.value1.total,
    servers.server2.asPercent.value1.total
    ...
    servers.serverN.asPercent.value1.total

Summary of Changes:
- Rename to groupByMultiNode
- Alias the resulting series so that it is easier to submit to other
  functions
- Add tests for series aliasing