jenkins master sometimes fails to add slave node

The addnode code often executes before the jenkins master service is fully started, resulting in:
    hook failed: "master-relation-changed"

Check & wait logic is needed there.

#### deployer fail
2014-10-01 14:44:47 [DEBUG] deployer.env: Connected to environment
2014-10-01 14:44:47 [INFO] deployer.import: Adding relations...
2014-10-01 14:44:47 [INFO] deployer.import: Adding relation osci:master <-> osci-slave:slave
2014-10-01 14:44:48 [DEBUG] deployer.import: Waiting for relation convergence 60s
2014-10-01 14:45:48 [ERROR] deployer.env: The following units had errors:
   unit: osci/0: machine: 1 agent-state: error details: hook failed: "master-relation-changed"
2014-10-01 14:45:48 [INFO] deployer.cli: Deployment stopped. run time: 539.98
Traceback (most recent call last):
  File "./deploy.py", line 632, in <module>
    main()
  File "./deploy.py", line 541, in main
    '-c', deployer_bundle])
  File "/usr/lib/python2.7/subprocess.py", line 540, in check_call
    raise CalledProcessError(retcode, cmd)

#### juju log
unit-osci-0: 2014-10-01 14:44:53 INFO master-relation-changed Adding node to Jenkins master
unit-osci-0: 2014-10-01 14:44:53 INFO master-relation-changed Traceback (most recent call last):
unit-osci-0: 2014-10-01 14:44:53 INFO master-relation-changed File "/var/lib/juju/agents/unit-osci-0/charm/hooks/addnode", line 18, in <module>
unit-osci-0: 2014-10-01 14:44:53 INFO master-relation-changed l_jenkins.create_node(host, int(executors) * 2, host , labels=labels)
unit-osci-0: 2014-10-01 14:44:53 INFO master-relation-changed File "/usr/lib/python2.7/dist-packages/jenkins/__init__.py", line 415, in create_node
unit-osci-0: 2014-10-01 14:44:53 INFO master-relation-changed raise JenkinsException('create[%s] failed'%(name))
unit-osci-0: 2014-10-01 14:44:53 INFO master-relation-changed jenkins.JenkinsException: create[osci-slave-0] failed
unit-osci-0: 2014-10-01 14:44:53 ERROR juju.worker.uniter uniter.go:486 hook failed: exit status 1

.

Digging a little deeper, simulating and re-creating: I restarted the master jenkins service, then immediately ran these commands, which expose 2 race scenarios:

#### jenkins master service is not started, no socket
ubuntu@juju-beis0-machine-1:~/tmp/charm/hooks$ ./addnode everywhere 2 qwerty ubuntu ubuntu
<jenkins.Jenkins object at 0x7fa96719c7d0>
Traceback (most recent call last):
  File "./addnode", line 16, in <module>
    if l_jenkins.node_exists(host):
  File "/usr/lib/python2.7/dist-packages/jenkins/__init__.py", line 355, in node_exists
    self.get_node_info(name)
  File "/usr/lib/python2.7/dist-packages/jenkins/__init__.py", line 338, in get_node_info
    response = self.jenkins_open(urllib2.Request(self.server + NODE_INFO%locals()))
  File "/usr/lib/python2.7/dist-packages/jenkins/__init__.py", line 174, in jenkins_open
    return urllib2.urlopen(req).read()
  File "/usr/lib/python2.7/urllib2.py", line 126, in urlopen
    return _opener.open(url, data, timeout)
  File "/usr/lib/python2.7/urllib2.py", line 400, in open
    response = self._open(req, data)
  File "/usr/lib/python2.7/urllib2.py", line 418, in _open
    '_open', req)
  File "/usr/lib/python2.7/urllib2.py", line 378, in _call_chain
    result = func(*args)
  File "/usr/lib/python2.7/urllib2.py", line 1207, in http_open
    return self.do_open(httplib.HTTPConnection, req)
  File "/usr/lib/python2.7/urllib2.py", line 1180, in do_open
    r = h.getresponse(buffering=True)
  File "/usr/lib/python2.7/httplib.py", line 1030, in getresponse
    response.begin()
  File "/usr/lib/python2.7/httplib.py", line 407, in begin
    version, status, reason = self._read_status()
  File "/usr/lib/python2.7/httplib.py", line 365, in _read_status
    line = self.fp.readline()
  File "/usr/lib/python2.7/socket.py", line 447, in readline
    data = self._sock.recv(self._rbufsize)
socket.error: [Errno 104] Connection reset by peer

#### jenkins master service is started, but not ready
ubuntu@juju-beis0-machine-1:~/tmp/charm/hooks$ ./addnode everywhere 2 qwerty ubuntu ubuntu
<jenkins.Jenkins object at 0x7f7b640587d0>
Adding node to Jenkins master
Traceback (most recent call last):
  File "./addnode", line 20, in <module>
    l_jenkins.create_node(host, int(executors) * 2, host , labels=labels)
  File "/usr/lib/python2.7/dist-packages/jenkins/__init__.py", line 415, in create_node
    raise JenkinsException('create[%s] failed'%(name))
jenkins.JenkinsException: create[everywhere] failed