environs/maas: fix provider config

environs/maas: fix provider config

[Note: this was originally proposed as lp:~rvb/juju-core/fix-maas-pvd-conf in the following MP:
https://code.launchpad.net/~rvb/juju-core/fix-maas-pvd-conf/+merge/158938
Due to issues with lbox, rvba asked me to submit this for him. No changes made, except
merging latest trunk.]

This branch fixes a problem we saw happening in the MAAS lab while testing the MAAS provider. The symptom was that, after having installed the bootstrap node ok, Juju was unable to deploy any service. The error found in the bootstrap node's logs: http://paste.ubuntu.com/5709878/.

The problem is that, from this code in cmd/jujud/upgrade.go: http://paste.ubuntu.com/5710182/, environs/maas/environ.go:SetConfig ends up being called on a nil object. After investigating the problem, I found that environs/maas/environprovider.go:Open(), when the config is invalid, returns a interface that has a nil value but a non-nil type (http://golang.org/doc/faq#nil_error) and thus, in cmd/jujud/upgrade.go (see snippet above), 'environ.SetConfig(cfg)' gets called on a nil 'environ'.

https://code.launchpad.net/~dimitern/juju-core/fix-maas-pvd-conf/+merge/158961

(do not edit description out of merge proposal)

[dimitern, 2013-04-15 15:46:06]

Please take a look.

[dimitern, 2013-04-15 15:49:28]

LGTM'ed already as
https://code.launchpad.net/~rvb/juju-core/fix-maas-pvd-conf/+merge/158938, so
I'm just going to submit it.

[dimitern, 2013-04-15 15:51:45]

*** Submitted:

environs/maas: fix provider config

[Note: this was originally proposed as lp:~rvb/juju-core/fix-maas-pvd-conf in
the following MP:
https://code.launchpad.net/~rvb/juju-core/fix-maas-pvd-conf/+merge/158938
Due to issues with lbox, rvba asked me to submit this for him. No changes made,
except
merging latest trunk.]

This branch fixes a problem we saw happening in the MAAS lab while testing the
MAAS provider. The symptom was that, after having installed the bootstrap node
ok, Juju was unable to deploy any service. The error found in the bootstrap
node's logs: http://paste.ubuntu.com/5709878/.

The problem is that, from this code in cmd/jujud/upgrade.go:
http://paste.ubuntu.com/5710182/, environs/maas/environ.go:SetConfig ends up
being called on a nil object. After investigating the problem, I found that
environs/maas/environprovider.go:Open(), when the config is invalid, returns a
interface that has a nil value but a non-nil type
(http://golang.org/doc/faq#nil_error) and thus, in cmd/jujud/upgrade.go (see
snippet above), 'environ.SetConfig(cfg)' gets called on a nil 'environ'.

R=
CC=
https://codereview.appspot.com/8772043