scan_coordinator: Add validation for scan parameters
scan_coordinator: Add validation for scan parameters

Change-Id: Ibb6f439f2107a266b0ed924fdfca234407d692b9
Reviewed-on: http://review.couchbase.org/43327
Reviewed-by: Sarath Lakshman <d41e430501c5d3aeeb2b91142f917f514040f807@couchbase.com>
Tested-by: Sarath Lakshman <d41e430501c5d3aeeb2b91142f917f514040f807@couchbase.com>

jchris/indexing,jchris/indexing,jchris/indexing,jchris/indexing