Reroute to primary and warn for mapreduce with out not 'inline'

This pull request is a suggestion for how we might reroute to the primary for the following command:

mapreduce with 'out' specified as something other than 'inline'

If this command is run with a non-primary read preference, it will be rerouted to the primary node and a warning will be logged:
"Database command 'mapreduce' rerouted to primary node"