Calls to krb5_principal_set_realm() can fail due to memory
allocation failures. If the client realm cannot be set in
the generated principal the wrong realm will be used.
Check for the result of krb5_principal_set_realm() and if
there is a failure, clean up and return the error code to
the caller.
Change-Id: Icadd04c858e88c1ba1d4344c60a784885a6a1344