DNS: check if DNS package is installed

Instead of separate checking of DNS required packages, we need just
check if IPA DNS package is installed.

https://fedorahosted.org/freeipa/ticket/4058

Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>
Reviewed-By: Petr Spacek <pspacek@redhat.com>
Reviewed-By: Tomas Babej <tbabej@redhat.com>

ipaplatform/base/constants.py

@@ -8,4 +8,4 @@ This base platform module exports platform dependant constants.
 
 
 class BaseConstantsNamespace(object):
-    pass
+    IPA_DNS_PACKAGE_NAME = "freeipa-server-dns"

ipaplatform/base/paths.py

@@ -218,6 +218,7 @@ class BasePathNamespace(object):
     GROUPADD = "/usr/sbin/groupadd"
     HTTPD = "/usr/sbin/httpd"
     IPA_CLIENT_INSTALL = "/usr/sbin/ipa-client-install"
+    IPA_DNS_INSTALL = "/usr/sbin/ipa-dns-install"
     SBIN_IPA_JOIN = "/usr/sbin/ipa-join"
     IPA_REPLICA_CONNCHECK = "/usr/sbin/ipa-replica-conncheck"
     IPA_RMKEYTAB = "/usr/sbin/ipa-rmkeytab"