Add dns check process

This lets us make sure we won't run tests if the DNS failed to update.
This will be much better than having giant spikes in the graphs when
things go wonky. Also, this will email me, so I won't have to check the
graphs every day to see if something broke on the DNS side of things.

srdnscheck.py

@@ -0,0 +1,53 @@
+#!/usr/bin/env python
+# This Source Code Form is subject to the terms of the Mozilla Public License,
+# v. 2.0. If a copy of the MPL was not distributed with this file, You can
+# obtain one at http://mozilla.org/MPL/2.0/.
+
+import logging
+import socket
+import sys
+
+import stoneridge
+
+
+def send_email():
+    myos = stoneridge.get_config('machine', 'os')
+    netconfig = stoneridge.get_config('run', 'netconfig')
+    srid = stoneridge.get_config('run', 'srid')
+
+    to = 'hurley@mozilla.com'
+    subject = 'DNS Update Failed'
+    msg = '''The DNS Update failed for the following run:
+        OS: %s
+        Netconfig: %s
+        SRID: %s
+    ''' % (myos, netconfig, srid)
+
+    stoneridge.sendmail(to, subject, msg)
+
+
+@stoneridge.main
+def main():
+    parser = stoneridge.ArgumentParser()
+    parser.parse_args()
+
+    logging.debug('Checking dns for example.com')
+    try:
+        ip = socket.gethostbyname('example.com')
+    except:
+        logging.exception('Error retrieving IP')
+        send_email()
+        sys.exit(1)
+
+    logging.debug('ip = %s' % (ip,))
+
+    bits = ip.split('.')
+    if bits[0] != '172':
+        logging.error('IP is not in 172/8')
+        send_email()
+        sys.exit(1)
+
+    if not (16 <= int(bits[1]) <= 31):
+        logging.error('IP is not in 172.16/12')
+        send_email()
+        sys.exit(1)

srworker.py

@@ -192,6 +192,8 @@ class StoneRidgeWorker(stoneridge.QueueListener):
 
         self.run_process('dnsupdater')
 
+        self.run_process('dnscheck')
+
         self.need_dns_reset = True
 
         self.run_process('runner')