jvm.gc stats fix for 0.90.x

This one should be what I originally intended for PR 12.

The jvm.gc.time and jvm.gc.count stats were being calculated in version-specific blocks. Where these stats are returned is either unrelated to the ElasticSearch version (and really a function of the jvm), or the style used in the ES 1.0 block is compatible with the 0.90 block.

We have both 1.0 and 0.90 hosts currently and this patch works with both versions, previously it broke with 0.90 servers.