Need a toy build to measure breakdown of persistence w/ xdcr

Hi Jin,

Created a bug to track the persistence breakdown on the source/xdcr.

thanks,
Ketaki

Need a toy build to measure breakdown of persistence on couchbase node.

• Measyre latency w/ disk write
• Measure disk Fetch

Add histogram for

• disk_write_queue
• Drain rate

"
At this point let's wait until ep engine (Jin) comes up with a way to measure latency for setMeta (with disk write), getMeta (with disk fetch), and total number of getMeta/setMeta. I will also add histogram for disk_write_queue and drain_rate as well."