Use dirty reads to get stats.
Use dirty reads to get stats.

According to the mnesia docs, dirty reads are ~10x as fast as reads
within a transaction. This should make the stats archiver more
responsive when a node gets slow.

Change-Id: Ib6353d344405fcefdb54fa41cd57bed283427e2c
Reviewed-on: http://review.northscale.com/2968
Tested-by: Steve Yen <ef850f73f7832052d3c6d9b5ddd3a1716d9a57f1@gmail.com>
Reviewed-by: Steve Yen <ef850f73f7832052d3c6d9b5ddd3a1716d9a57f1@gmail.com>

ceejatec/ns_server,t3rm1n4l/ns_server,daverigby/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,mschoch/ns_server,mschoch/ns_server,mschoch/ns_server,pavel-blagodov/ns_server,ceejatec/ns_server,daverigby/ns_server,membase/ns_server,nimishzynga/ns_server,daverigby/ns_server,nimishzynga/ns_server,membase/ns_server,pavel-blagodov/ns_server,ceejatec/ns_server,t3rm1n4l/ns_server,mschoch/ns_server,mschoch/ns_server,membase/ns_server,pavel-blagodov/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,pavel-blagodov/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,vzasade/ns_server,membase/ns_server,daverigby/ns_server,ceejatec/ns_server,membase/ns_server,vzasade/ns_server,vzasade/ns_server,ceejatec/ns_server,membase/ns_server,daverigby/ns_server,t3rm1n4l/ns_server,vzasade/ns_server,nimishzynga/ns_server