Revert "CDH-18751: Impala should use a unique Kerberos credentials cache location"

This reverts commit 36327bd74c76dc69207d148cc401190fe5a9a50c.

Change-Id: I2a7fc745f24f851cf87a8b7e6c6525530cb958f7
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2450
Tested-by: jenkins
Reviewed-by: Henry Robinson <henry@cloudera.com>