Make most commands re-tryable, and a few that won't be re-tried [JIRA: CLIENTS-776]

[lukebakken]

basho/riak-go-client#53, basho/riak-go-client#56

Some commands should not be retried if an error occurs, due to the load placed on Riak:

• Map/Reduce
• List Keys
• List Buckets
• YZ Search
• Secondary Index Query