MB-5505: Make sure we do not over-split the VB list
MB-5505: Make sure we do not over-split the VB list

Today when XDCR is scheduling replication, it splits the vbucket list
into two [list1, list2] where length of list1 is number of concurrent
replication streams defined in an env parameter. But there could
be a case that the parameter value is greater than the length of
vbucket list. This changeset will fix this issue by determing the
right position to split the vbucket list.

Change-Id: I32a84b8082114bc39e13e34338d9d9d882196080
Reviewed-on: http://review.couchbase.org/17169
Reviewed-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Tested-by: Junyi Xie <cec9b1c9f34a8d92cba938f3f3364d5120580782@gmail.com>

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