Increase default +zdbbl setting from 1MB to 32MB

Fixes: basho/riak#445
Merge pull request #518 from basho/jem-increase-defaul-zdbbl

Increase default +zdbbl setting from 1MB to 32MB
Merge pull request #516 from basho/rz/feature/yz-aae-status

Add riak-admin search subcommand
Add switch-to-new-search command

Add the switch-to-new-search command under the search command. This is
used when migrating from legacy riak_search to yokozuna. It does a
multicall across the cluster handing over HTTP and PB control from
riak_search to yokozuna.