ansible_module_utils: add method to retrive SID from dom_name.

When managing idranges, it might be needed to obtain the domain SID
from the domain name. As this method needs to use the IPA API object
and requires imorting some ipaserver modules, teh best place for this
method to be implemented is on ansible_module_utils.

plugins/module_utils/ansible_freeipa_module.py

@@ -139,6 +139,13 @@ else:
 
                 return fstore.has_files()
 
+    # Try to import dcerpc
+    try:
+        import ipaserver.dcerpc  # pylint: disable=no-member
+        _dcerpc_bindings_installed = True  # pylint: disable=invalid-name
+    except ImportError:
+        _dcerpc_bindings_installed = False  # pylint: disable=invalid-name
+
     if six.PY3:
         unicode = str
 
@@ -221,6 +228,8 @@ else:
                 ldap_cache: Control use of LDAP cache layer. (bool)
 
         """
+        global _dcerpc_bindings_installed  # pylint: disable=C0103,W0603
+
         env = Env()
         env._bootstrap()
         env._finalize_core(**dict(DEFAULT_CONFIG))
@@ -252,6 +261,7 @@ else:
             backend = api.Backend.ldap2
         else:
             backend = api.Backend.rpcclient
+            _dcerpc_bindings_installed = False
 
         if not backend.isconnected():
             backend.connect(ccache=os.environ.get('KRB5CCNAME', None))
@@ -701,6 +711,40 @@ else:
         print(jsonify(kwargs))
         sys.exit(0)
 
+    def __get_domain_validator():
+        if not _dcerpc_bindings_installed:
+            raise ipalib_errors.NotFound(
+                reason=(
+                    'Cannot perform SID validation without Samba 4 support '
+                    'installed. Make sure you have installed server-trust-ad '
+                    'sub-package of IPA on the server'
+                )
+            )
+
+        domain_validator = ipaserver.dcerpc.DomainValidator(api)
+
+        if not domain_validator.is_configured():
+            raise ipalib_errors.NotFound(
+                reason=(
+                    'Cross-realm trusts are not configured. Make sure you '
+                    'have run ipa-adtrust-install on the IPA server first'
+                )
+            )
+
+        return domain_validator
+
+    def get_trusted_domain_sid_from_name(dom_name):
+        """
+        Given a trust domain name, returns the domain SID.
+
+        Returns unicode string representation for a given trusted domain name
+        or None if SID for the given trusted domain name could not be found.
+        """
+        domain_validator = __get_domain_validator()
+        sid = domain_validator.get_sid_from_domain_name(dom_name)
+
+        return unicode(sid) if sid is not None else None
+
     class IPAParamMapping(Mapping):
         """
         Provides IPA API mapping to playbook parameters or computed values.