Fix two HBase store name shortening bugs

* Prior to commit, the short version of lock store names were strings
  like "v_lock_" whereas the desired name is a single character like
  "w".  This was caused by Backend generating lock store names by
  calling store.getName() on the non-lock counterpart and appending
  the lock suffix.  Now HBase remembers the store name originally used
  to open the database and returns it from getName().

* Fixed bug where HBaseStoreManager would open a new store instance
  every time openDatabase(s) was called for some fixed string s when
  CF name shortening was enabled.  I think this was harmless from a
  correctenss point of view, but it needlessly wasted memory.
Merge branch 'master' of github.com:thinkaurelius/titan