Admission controller: Fix exception message when llama-site cannot be found

We no longer look for files on the classpath, we just try to find the file
specified as it is.

Change-Id: I127f508ff6b91f671385985d32b7898b208ae2ed
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1895
Reviewed-by: Alex Behm <alex.behm@cloudera.com>
Tested-by: jenkins