Add list of domains associated to our realm to cn=etc

Add new LDAP container to store the list of domains associated with IPA realm.
Add two new ipa commands (ipa realmdomains-show and ipa realmdomains-mod) to allow
manipulation of the list of realm domains.
Unit test file covering these new commands was added.

https://fedorahosted.org/freeipa/ticket/2945

install/updates/40-realm_domains.update

@@ -0,0 +1,8 @@
+# Add the Realm Domains container
+
+dn: cn=Realm Domains,cn=ipa,cn=etc,$SUFFIX
+default:objectClass: domainRelatedObject
+default:objectClass: nsContainer
+default:objectClass: top
+default:cn: Realm Domains
+default:associatedDomain: $DOMAIN

install/updates/Makefile.am

@@ -28,6 +28,7 @@ app_DATA =				\
 	25-referint.update		\
 	30-s4u2proxy.update		\
 	40-delegation.update		\
+	40-realm_domains.update		\
 	40-replication.update		\
 	40-dns.update			\
 	40-automember.update		\