Remove duplication of datanode network addresses in HdfsTable

This removes duplication TNetworkAddresses in the block location metadata of HdfsTable.
Each HdfsTable now contains a list of TNetworkAddress and the BlockLocations
just reference an index in this list to specify the host, rather than duplicating the
TNetworkAddress.

For a table with 100K blocks, this reduces the size of the THdfsTable struct by an additional
~50+% (on top of the duplicate file path changes). This takes the total size of the table
from:
21.1MB -> 9.4MB (file path duplication) -> 4.2MB (host duplication) = ~80% total improvement.

Change-Id: If7f11764dc0961376f9648779d253829f4cd83a2
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1367
Reviewed-by: Lenni Kuff <lskuff@cloudera.com>
Tested-by: jenkins