Initial work on client performance improvement fix
WIP
Fixed problem with MultiMap contains methods

Also added a test that verifies that a HZ cluster works fine with dumb clients and the performance improvement.
Minor checkstyle related fixes
Fixed import issue due to merging
Processed review comments + did minor cleanup on the heartbeat monitor.
Merge pull request #3263 from pveentjer/performance/3.x/client2

Performance/3.x/client2