method Client.AddMachinesV2 is not implemented

[Curtis Hovey]

The compatibility-control job used to certify that mixed versions of juju servers and clients can work failed. A 1.18.4 env was bootstrapped, then the 1.21-alpha2 client was used to maintain the env. This simulates a case where user machines get the future 1.21.0 but the enterprise still has 18.x envs.
    http://juju-ci.vapour.ws:8080/job/compatibility-control/48/console
    http://juju-ci.vapour.ws:8080/job/compatibility-control/50/console

The specific issue is this from the console log:
juju --show-log add-machine -e compatibility-control lxc
2014-09-23 19:05:05 INFO juju.cmd supercommand.go:37 running juju [1.21-alpha2-precise-amd64 gc]
2014-09-23 19:05:05 INFO juju.api api.go:234 connecting to API addresses: [ec2-54-164-24-66.compute-1.amazonaws.com:17070]
2014-09-23 19:05:05 INFO juju.api apiclient.go:252 dialing "wss://ec2-54-164-24-66.compute-1.amazonaws.com:17070/"
2014-09-23 19:05:05 INFO juju.api apiclient.go:175 connection established to "wss://ec2-54-164-24-66.compute-1.amazonaws.com:17070/"
2014-09-23 19:05:05 ERROR juju.cmd supercommand.go:323 no such request - method Client.AddMachinesV2 is not implemented

The inverse is also broken when an 1.18.x client talks to a 1.21x
    http://juju-ci.vapour.ws:8080/job/compatibility-control/49/console

juju --show-log add-machine -e compatibility-control lxc
2014-09-23 19:15:05 INFO juju.cmd supercommand.go:297 running juju-1.18.1-precise-amd64 [gc]
2014-09-23 19:15:05 INFO juju api.go:238 connecting to API addresses: [ec2-54-210-53-115.compute-1.amazonaws.com:17070 ip-172-31-9-149.ec2.internal:17070 54.210.53.115:17070 172.31.9.149:17070]
2014-09-23 19:15:05 INFO juju apiclient.go:114 state/api: dialing "wss://ec2-54-210-53-115.compute-1.amazonaws.com:17070/"
2014-09-23 19:15:05 INFO juju apiclient.go:124 state/api: connection established
2014-09-23 19:15:09 ERROR juju.cmd supercommand.go:300 EOF

This regression may have been in place for a while. The test was updated to try add machine this week.

[Dimiter Naydenov (dimitern)]

The problem happens due to prematurely removing the 1.18 compatibility code in https://github.com/juju/juju/pull/308, more specifically in this commit https://github.com/juju/juju/commit/515715ccc71cec662625caef7eba60a97c6b9e80.

The solution is to reintroduce the compatibility code.