Fix PKCS11 helper

Slots in HSM are not assigned statically, we have to chose proper
slot from token label.

Softhsm i2.2.0 changed this behavior and now slots can change over
time (it is allowed by pkcs11 standard).

Changelog:
* created method get_slot() that returns slot number from
  used label
* replaces usage of slot in __init__ method of P11_Helper
  with label
* slot is dynamically detected from token label before
  session is opened
* pkcs11-util --init-token now uses '--free' instead '--slot'
  which uses first free slot (we don't care about slot numbers
  anymore)

https://pagure.io/freeipa/issue/6692

Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>

daemons/dnssec/ipa-dnskeysync-replica

@@ -15,6 +15,7 @@ import os
 import sys
 
 import ipalib
+from ipalib.constants import SOFTHSM_DNSSEC_TOKEN_LABEL
 from ipalib.install.kinit import kinit_keytab
 from ipapython.dn import DN
 from ipapython.ipa_log_manager import root_logger, standard_logging_setup
@@ -158,8 +159,7 @@ ldapkeydb = LdapKeyDB(log, ldap,
         DN(('cn', 'keys'), ('cn', 'sec'), ipalib.api.env.container_dns,
            ipalib.api.env.basedn))
 
-# TODO: slot number could be configurable
-localhsm = LocalHSM(paths.LIBSOFTHSM2_SO, 0,
+localhsm = LocalHSM(paths.LIBSOFTHSM2_SO, SOFTHSM_DNSSEC_TOKEN_LABEL,
         open(paths.DNSSEC_SOFTHSM_PIN).read())
 
 ldap2replica_master_keys_sync(log, ldapkeydb, localhsm)

daemons/dnssec/ipa-ods-exporter

@@ -32,6 +32,7 @@ import sqlite3
 import traceback
 
 import ipalib
+from ipalib.constants import SOFTHSM_DNSSEC_TOKEN_LABEL
 from ipalib.install.kinit import kinit_keytab
 from ipapython.dn import DN
 from ipapython import ipaldap
@@ -647,7 +648,7 @@ log.debug('Connected')
 ldapkeydb = LdapKeyDB(log, ldap, DN(('cn', 'keys'), ('cn', 'sec'),
                                     ipalib.api.env.container_dns,
                                     ipalib.api.env.basedn))
-localhsm = LocalHSM(paths.LIBSOFTHSM2_SO, 0,
+localhsm = LocalHSM(paths.LIBSOFTHSM2_SO, SOFTHSM_DNSSEC_TOKEN_LABEL,
         open(paths.DNSSEC_SOFTHSM_PIN).read())
 
 ldap2master_replica_keys_sync(log, ldapkeydb, localhsm)