classic snap are missing some env variables for reaching command name. (snap build, executing it fails)

1. Classic snap, where snapcraft.yaml can be found on lp:~didrocks/+junk/chuck-norris-webserver-classic.
2. Note that it declares and builds ok:
apps:
  node-service:
    command: chuck-norris-app
    daemon: simple
    restart-condition: always
  cli:
    command: chuck-norris-cli
3. Building and installing, executing:
$ chuck-norris-webserver-classic.cli
/snap/chuck-norris-webserver-classic/x2/command-cli.wrapper: 2: exec: chuck-norris-cli: not found

The issue is that indeed, the wrapper don't add $SNAP/bin/ to $PATH:
#!/bin/sh
exec "chuck-norris-cli" "$@"

The non classic version works as it does add it to the path.

Note that specifying "bin/chuck-norris-cli" instead of just "chuck-norris-cli" works in classic and generate something like:
exec "$SNAP/bin/node" "$SNAP/bin/chuck-norris-cli" "$@"

4. Another side effect is that it's not the snap node version which is used in that case. The script declares "#!/usr/bin/env node" resolving to system one.
#!/bin/sh
exec "chuck-norris-cli" "$@"
-> will resolve to the system one, while if specified as bin/chuck-norris-cli:
exec "$SNAP/bin/node" "$SNAP/bin/chuck-norris-cli" "$@"

I would expect in both case to prefer the snap version.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: snapcraft 2.27.1 [modified: usr/lib/python3/dist-packages/snapcraft/_baseplugin.py usr/lib/python3/dist-packages/snapcraft/plugins/python.py]
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: Mon Mar 6 16:06:59 2017
InstallationDate: Installed on 2012-05-28 (1743 days ago)
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
PackageArchitecture: all
SourcePackage: snapcraft
UpgradeStatus: Upgraded to xenial on 2014-10-31 (857 days ago)