Don't create a separate process to merge backup files.
Don't create a separate process to merge backup files.

Creating a separate process to merge incremental backup files
slows down the merge performance significantly. This patch
performs the merge operations within the same python process.

Change-Id: Id670ece92aa6d8d60acf113f97a6df8a7e543bcd
Reviewed-on: http://review.couchbase.org/12040
Reviewed-by: Steve Yen <ef850f73f7832052d3c6d9b5ddd3a1716d9a57f1@gmail.com>
Tested-by: Chiyoung Seo <8b279095f11c26cc21045fda5a3e51debb005aa9@gmail.com>

teligent-ru/ep-engine,sriganes/ep-engine,membase/ep-engine,daverigby/kv_engine,couchbaselabs/ep-engine,daverigby/ep-engine,hisundar/ep-engine,sriganes/ep-engine,daverigby/ep-engine,daverigby/kv_engine,couchbase/ep-engine,abhinavdangeti/ep-engine,owendCB/ep-engine,sriganes/ep-engine,couchbaselabs/ep-engine,owendCB/ep-engine,abhinavdangeti/ep-engine,daverigby/ep-engine,couchbase/ep-engine,abhinavdangeti/ep-engine,daverigby/kv_engine,zbase/ep-engine,hisundar/ep-engine,hisundar/ep-engine,teligent-ru/ep-engine,owendCB/ep-engine,zbase/ep-engine,membase/ep-engine,couchbaselabs/ep-engine,zbase/ep-engine,zbase/ep-engine,jimwwalker/ep-engine,membase/ep-engine,zbase/ep-engine,teligent-ru/ep-engine,abhinavdangeti/ep-engine,owendCB/ep-engine,daverigby/kv_engine,couchbaselabs/ep-engine,couchbase/ep-engine,membase/ep-engine,jimwwalker/ep-engine,hisundar/ep-engine,daverigby/ep-engine,jimwwalker/ep-engine,couchbase/ep-engine,teligent-ru/ep-engine,couchbaselabs/ep-engine,sriganes/ep-engine,jimwwalker/ep-engine,abhinavdangeti/ep-engine