Enable lazy loading of table metadata for the CatalogService/Impalad

This change adds support for lazy loading of table metadata to the
CatalogService/Impalad. The way this works is that the CatalogService initially
sends out an update with only the databases and table names (wrapped as
IncompleteTables). When an Impalad encounters one of these tables, it will contact
the catalog service to get the metadata, possibly triggering a metadata load if the
catalog server has not yet loaded this table.

With these changes the catalog server starts up in just seconds, even for large
metastores since it only needs to call into the metastore to get the list of tables
and databases. The performance of "invalidate metadata" also improves for the same reason.

I also picked up the catalog cleanup patch I had to make the APIs a bit more consistent and
remove the need for using a LoadingCache for databases.

This also fixes up the FE tests to run in a more realistic fashion. The FE tests now run
against catalog object recieved from the catalog server. This actually turned up some bugs
in our previous test configuration where we were not running with the correct column stats
(we were always running with avgSerializedSize = slotSize).  This changed some plans so the
planner tests needed to be updated.

Still TODO:
This does not include the changes to perform background metadata loading. I will send
that out as a separate patch on top of this.

Change-Id: Ied16f8a7f3a3393e89d6bfea78f0ba708d0ddd0e
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1266
Tested-by: Lenni Kuff <lskuff@cloudera.com>
Reviewed-by: Lenni Kuff <lskuff@cloudera.com>