MB-100: XDCRtests:  Replication type def. settings

- Replication type defaults to "capi" mode
- To have your tests pick up "xmem" mode, please
set variable "replication_type" to "xmem" on your tests

Change-Id: Ic7d48e51be10b74e4c22a6220f19bb66900be8a4
Reviewed-on: http://review.couchbase.org/28795
Reviewed-by: abhinav dangeti <abhinav.dangeti@gmail.com>
Tested-by: abhinav dangeti <abhinav.dangeti@gmail.com>