IMPALA-934: Refresh cached UDF library when creating a new function

This change adds the ability to refresh a local cache entry, causing
the old cache entry to be dropped and the library to be reloaded from
HDFS. This is used in ResolveSymbolLookup(), which is called by the
frontend when creating a new a function, and in ImpalaServer when
receiving a "create function" heartbeat. This change also makes sure
the FE calls into the backend for jars, so jars get refreshed as well.

Change-Id: I5fd61c1bc2e04838449335d5a68b61af8b101b01
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2286
Reviewed-by: Skye Wanderman-Milne <skye@cloudera.com>
Tested-by: jenkins