SERVER-63495 linked cluster find, aggregate, getMore, insert, update and delete into mongod. It relies on calling Impl::checkCanRunHere() to prevent these commands from being run on a non-shardsvr mongod. However, currently this method is not called in the explain() method for ClusterWriteCmd and ClusterPipelineCommandBase so right now the explain command for cluster write and cluster aggregate can be invoked on non-shardsvr mongod. As shown in BF-26337, running it causes the mongod to hit a segmentation fault.