Handle various forms of admin accounts when establishing trusts

Realm administrator account may be specified using different form:
Administrator, DOM\Administrator, Administrator@DOMAIN

This patch introduces handling of the second two forms:
- In DOM\Administrator only user name is used, short domain name
  is then taken from a discovered record from the AD DC
- In Administrator@DOMAIN first DOMAIN is verified to be the same
  as the domain we are establishing trust to, and then user name
  is taken, together with short domain name taken from a discovered
  record from the AD DC

Note that we do not support using to-be-trusted domain's trusted domains'
accounts to establish trust as there is basically zero chance to verify
that things will work with them. In addition, in order to establish trust
one needs to belong to Enterprise Admins group in AD or have specially
delegated permissions. These permissions are unlikely delegated to the
ones in already trusted domain.

https://fedorahosted.org/freeipa/ticket/2864

ipalib/plugins/trust.py

@@ -180,6 +180,14 @@ class trust_add(LDAPCreate):
         # generate random trustdom password to do work on both sides
         if 'realm_admin' in options:
             realm_admin = options['realm_admin']
+            names = realm_admin.split('@')
+            if len(names) > 1:
+                # realm admin name is in UPN format, user@realm, check that
+                # realm is the same as the one that we are attempting to trust
+                if keys[-1].lower() != names[-1].lower():
+                    raise errors.ValidationError(name=_('AD Trust setup'),
+                                 error=_('Trusted domain and administrator account use different realms'))
+                realm_admin = names[0]
 
             if 'realm_passwd' not in options:
                 raise errors.ValidationError(name=_('AD Trust setup'), error=_('Realm administrator password should be specified'))

ipaserver/dcerpc.py

@@ -363,6 +363,11 @@ class TrustDomainJoins(object):
         rd.read_only = True
         if realm_admin and realm_passwd:
             if 'name' in rd.info:
+                names = realm_admin.split('\\')
+                if len(names) > 1:
+                    # realm admin is in DOMAIN\user format
+                    # strip DOMAIN part as we'll enforce the one discovered
+                    realm_admin = names[-1]
                 auth_string = u"%s\%s%%%s" % (rd.info['name'], realm_admin, realm_passwd)
                 td = get_instance(self)
                 td.creds.parse_string(auth_string)