Modify default values for XDCR Capi settings ( Source and Target nozzles)

Often users notice issues when using the default Source/Target Nozzle settings to a remote ES cluster. The remote ES cluster is unable to keep up with the incoming xdcr and shows error on indexing with 'too many concurrent requests'. There is little to no ES indexing activity on the target ES cluster.

Default Value : Source nozzle 2, Target nozzle 2
Type of XDCR Replication : CAPI

Logs from ES node
Too many concurrent requests. _bulk_docs requests: 1004, _revs_diff requests: 20, Max configured: 1024

Most cases tuning this value to a lower number Source nozzle 1, Target nozzle 1
enables the ES indexing to continue as expected in a successful fashion.

It would be good to make this value "1" as default for Source/Target nozzle settings and/or test for another better value.