snappy should not claim to install/remove before validating provided package name

[James Hunt]

ubuntu@localhost:~$ sudo snappy install moo
Installing moo
No package '' for ubuntu-core/devel-proposed

ubuntu@localhost:~$ sudo snappy remove moo
Removing moo
snappy package not found

The current behaviour is misleading since the user -- fleetingly -- believes the operation will progress. I think we should change the behaviour to only emit the "Installing" / "Removing" message once the package has been validated:

ubuntu@localhost:~$ sudo snappy install moo
No package '' for ubuntu-core/devel-proposed
ubuntu@localhost:~$ sudo snappy install docker
Installing docker

ubuntu@localhost:~$ sudo snappy remove moo
snappy package not found
ubuntu@localhost:~$ sudo snappy remove docker
Removing docker

_____
(Note the "No package ''..." is fixed by https://code.launchpad.net/~jamesodhunt/snappy/dont-clobber-pkgname-if-pkg-ENOENT/+merge/255052).

[Michael Vogt (mvo)]

This is no longer printed in the snappy 16 series.