krb5_cc_end_seq_get() is not expected to fail because it is a
cleanup routine. If it fails it indicates something wrong with
the cache or the system. Return the failure if there is one.
Otherwise, the failure from krb5_cc_next_cred() should be
returned UNLESS it is KRB5_CC_END in which case return success.
Change-Id: I80e07103e2fb38aa40418a436fa5351fb89549d3