CBD-399: bump up default MAX_CONCURRENT_REPS_PER_DOC to 32
CBD-399: bump up default MAX_CONCURRENT_REPS_PER_DOC to 32

Given all recent changes to push up XDCR performance, there is no
need to limit only 8 concurrent replicatons per bucket.

Change-Id: Iee196c8922a9f4397dc256dfd0a8972e5799d8c5
Reviewed-on: http://review.couchbase.org/19929
Reviewed-by: Ketaki Gangal <c7141f0717da6f2e739c31892f081a1a527a34e4@gmail.com>
Reviewed-by: Pavel Paulau <dd88eded64e90046a680e3a6c0828ceb8fe8a0e7@gmail.com>
Reviewed-by: Junyi Xie <cec9b1c9f34a8d92cba938f3f3364d5120580782@gmail.com>
Tested-by: Junyi Xie <cec9b1c9f34a8d92cba938f3f3364d5120580782@gmail.com>

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