improvement(get_ldap_config): rename function
improvement(get_ldap_config): rename function

because we added a `get_ldap_ms_ad_config`, it
doesn't make sense the other function to be
called `get_ldap_config`, and it was now renamed
to be `get_openldap_config` to reflect better
what kind of LDAP configuration it is (specially
if in the future other back end LDAP servers
will be added).

scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-longevity-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests