Fixed lp:1635464: infinite recursion in worker/peergroper

[dimitern]

When validating the "mongo" space name (common among all controllers),
the way stateShim.Space() was implemented in worker/peergrouper/shim.go
caused infinite recursion when called. This fixes http://pad.lv/1635464.

While I couldn't reproduce this normally, it's easy to trigger the case
when state.ControllerInfo.MongoSpaceState is "valid" by modifying the
mongo controllers collection directly.

QA steps (if you do those same steps without the fix, the bug happens):

1. juju bootstrap vmaas-21 m21
2. juju switch controller
3. juju ssh 0
4. ubuntu@maas-21-node-0:~$ sudo grep 'fatal error: stack overflow' /var/log/juju/machine-0.log

   verify no matches are found initially

5. ubuntu@maas-21-node-0:~$ export STATE_PASSWORD=$(sudo grep statepassword: /var/lib/juju/agents/machine-0/agent.conf | cut -b16-)
6. ubuntu@maas-21-node-0:~$ sudo /usr/lib/juju/mongo3.2/bin/mongo 127.0.0.1:37017/admin --ssl --sslAllowInvalidCertificates --sslPEMKeyPassword /var/lib/juju/shared-secret --sslPEMKeyFile /var/lib/juju/server.pem -u machine-0 -p $STATE_PASSWORD
7. Run the following commands in the mongo shell:
   juju:PRIMARY> use juju;
   juju:PRIMARY> db.controllers.update({_id:"e"}, {"$set": {"mongo-space-name": "space-0", "mongo-space-state": "valid"}})

   output: WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })

   juju:PRIMARY> exit;
8. ubuntu@maas-21-node-0:~$ sudo grep 'selecting mongo peer hostPort in space space-0 from' /var/log/juju/machine-0.log

   verify the peergrouper picked up the change (>1 matches expected)

9. ubuntu@maas-21-node-0:~$ sudo grep 'fatal error: stack overflow' /var/log/juju/machine-0.log

   verify the bug does not occur after the changes

[frankban]

Looks good, and the method is defined (even if State is embedded) for testing/stubbing purposes I guess. Thank you!

[perrito666]

I am worried that this change touches no tests, even thiugh it is impractical to test for coding errors it is mote worthy that there seems to be no test exercising this path in a way that triggers the previous error.

[dimitern]

$$fixes-1635464$$

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju

[jujubot]

Build failed: Tests failed
build url: http://juju-ci.vapour.ws:8080/job/github-merge-juju/9554

[dimitern]

$$again$$

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju