replaced cache miss % with disk reads
replaced cache miss % with disk reads

Change-Id: I31c672e303caac140bbc0071760d1542ff860fe1
Reviewed-on: http://review.membase.org/4447
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Benjamin Young <399aded95f850edb83f13cae14dbe3e10ed19071@bigbluehat.com>
Reviewed-by: Dale Harvey <491ccac09a36ad1e38b698f273b84fd8efc31071@arandomurl.com>
Reviewed-by: Sean Lynch <e07ca8b5c22e6f6609daf94a8bc7d7ee0eb3f49b@gmail.com>

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