Incomplete error message on transition from strict to classic confinement

[Celso Providelo]

While verifying the correct behavior of transition from strict to classic confinement in the Store we got the following sequence:

{{{
$ snap --version
snap 2.26.4
snapd 2.26.4
series 16
ubuntu 16.04
kernel 4.4.0-79-generic

$ snap remove hello-noise && snap install hello-noise --revision 1 && snap refresh hello-noise
hello-noise removed
hello-noise 0.1 from 'noise' installed
error: This revision of snap "" was published using classic confinement and thus may perform
       arbitrary system changes outside of the security sandbox that snaps are usually confined to,
       which may put your system at risk.

       If you understand and want to proceed repeat the command including --classic.

$ snap remove hello-noise && snap install hello-noise
hello-noise removed
error: This revision of snap "hello-noise" was published using classic confinement and thus may
       perform arbitrary system changes outside of the security sandbox that snaps are usually
       confined to, which may put your system at risk.

       If you understand and want to proceed repeat the command including --classic.
}}}

The snap name is not replaced properly when the error is identified in the refresh operation and it works fine when identified in the install operation. I suspect refresh is not getting all the data (fields) it needs from the refresh store responses.

This more complete error message was introduced in 2.26, previous versions use a simpler form where the problem is not evident.