kt_renewer doesn't work for root user

The Krb credential cache is stored as "/tmp/hue_krb5_ccache_%d" % os.geteuid(), which creates inconsistency when Hue is started by root.

When the root user starts Hue, the cpserver would see euid root, but the kt_renewer would see euid hue. This is because the kt_renewer drops root and the cpserver doesn't (from the supervisor's point of view). I'm proposing that we set the cache path to a simple static path.

[Issue reported by ATM.]