Fix KCM retrieval support for sssd

Fix KCM retrieval support for sssd

Commit 795ebba8c039be172ab93cd41105c73ffdba0fdb added a retrieval
handler using KCM_OP_RETRIEVE, falling back on the same error codes as
the previous KCM_OP_GET_CRED_LIST support.  But sssd (as of 2.4)
returns KRB5_CC_NOSUPP instead of KRB5_CC_IO if it recognizes an
opcode but does not implement it.  Add a helper function to recognize
all known unsupported-opcode error codes, and use it in kcm_retrieve()
and kcm_start_seq_get().

ticket: 8997