Creation of DNS Dig tool

* Creation of module dns_dig
* Added dig and dig_search functions
* dig uses dnspython package to query
  the given url and return the target
  from the answer.
* dig_search will recursively call dig
  to look for a search string amount the
  urls that dig finds.
* Updated pip-requires to add dnspython

Change-Id: I6393c52f4f8b903dff100569d3be59f970d56f95

cloudcafe/common/tools/dns_dig.py

@@ -0,0 +1,45 @@
+"""
+Copyright 2016 Rackspace
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+"""
+import re
+from dns import resolver
+
+
+def dig(url, dig_type=None):
+    """
+    Use dns.resolver to query the provided url and return the target from the
+    answer. Resolver will raise an exception if no Answer is returned from the
+    query.
+    """
+    for rdata in resolver.query(url, dig_type):
+        return rdata.target
+
+
+def dig_search(url, search_string=None):
+    """
+    Recursively digs URL's until one with the specified search string is
+    found. Otherwise return None.
+    """
+    url = str(url)
+
+    if re.search(search_string, url):
+        # Found search string in url, return it
+        return url
+    elif not url:
+        return
+    else:
+        # Dig on the url
+        url = dig(url, dig_type="cname")
+        return dig_search(url, search_string)

pip-requires

@@ -2,3 +2,4 @@ IPy
 netaddr
 XenAPI
 dateutils
+dnspython