Moved _close test to end, and implemented _stats API call

Moved fixed _close test to the end so others don't failed on a closed index, and implemented _stats API call + test.

Sorry for the mess - don't think I can push to https://github.com/phillro/node-elasticsearch-client/pull/76 since it shows as merged.

Change-Id: Ibefcf58d732b970f91bc3e999e7600eed3850710