Data structure to hold HRegionInfo and the address for the hosting
HRegionServer. Immutable. Comparable, but we compare the 'location' only:
i.e. the hostname and port, and *not* the regioninfo. This means two
instances are the same if they refer to the same 'location' (the same
hostname and port), though they may be carrying different regions.
On a big cluster, each client will have thousands of instances of this object, often
100 000 of them if not million. It's important to keep the object size as small