InMemoryMapIT has a few bugs

When elserj was merging in ACCUMULO-4148, he found a couple of small issues that need to be fixed.

• Use multiple locality groups at https://github.com/apache/accumulo/blob/1.6/test/src/test/java/org/apache/accumulo/test/InMemoryMapIT.java#L305
• LocalityGroupMapWithNative should use 'true' to actually make a native map

Can use the constants at https://github.com/apache/accumulo/blob/1.6/server/tserver/src/main/java/org/apache/accumulo/tserver/InMemoryMap.java#L198 to verify the correct maps are created.