com.hazelcast.client test cleanup (packages atomiclong to map)

Cleanup for the first 11 test packages in com.hazelcast.client (excluding executor, which is cleaned in https://github.com/hazelcast/hazelcast/pull/2950).

Removed (mostly) generic warnings. Renamed @Before[Class] and @After[Class] functions. Renamed one-character-variables. Renamed variables instance/hz/something[1-9] to server/client[1-9]. Removed final from variables and parameters where suitable. Changed visibility and static of members and functions. Cleanup of imports. Made some whitespace changes and re-arrangements in the code.

One test seems to fails constantly, although it's not marked as ProblematicClass. It fails in the actual master branch as well, so this should not be related to changes in this PR (ClientExecutionPoolSizeLowTest.testOwnerNodeTerminateWithAsyncOperations()).
I would use UsernamePasswordCredentials.class.getName instead of hardcoding the string. But this was code you didn't write, just reformatted.