Can't reinstall a snap already installed switching confinement mode

[Didier Roche-Tolomelli]

Say I'm installing the hello snap, confined:
1. snap install hello
Trying then to reinstall it in devmode:
2. snap install --devmode hello
snap "hello" is already installed, see "snap refresh --help"

I find the user message confusing. The current confinement mode should maybe be written and a more defined help (telling to use refresh --<confinement_mode>) to switch mode will help better in guiding the user.
We can as well infer what the user intents here, and just switch confinement mode, without asking her/him to run another command as we got exactly what she/he wanted.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: snapd 2.22.3
ProcVersionSignature: Ubuntu 4.4.0-64.85-generic 4.4.44
Uname: Linux 4.4.0-64-generic x86_64
NonfreeKernelModules: zfs zunicode zcommon znvpair zavl
ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
CurrentDesktop: Unity
Date: Wed Mar 1 15:46:50 2017
InstallationDate: Installed on 2012-05-28 (1738 days ago)
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
SourcePackage: snapd
UpgradeStatus: Upgraded to xenial on 2014-10-31 (852 days ago)

[Bryan Larsen (bryan-larsen)]

snap refresh doesn't work either:

snap refresh --devmode maas
snap "maas" has no updates available