snapcraft dependencies are too big

[Sergio Schvezov]

These are the current dependencies:

Depends: bzr,
         dpkg-dev,
         git,
         mercurial,
         python3-apt,
         python3-docopt,
         python3-jsonschema,
         python3-lxml,
         python3-pkg-resources,
         python3-requests,
         python3-requests-oauthlib,
         python3-ssoclient,
         python3-xdg,
         python3-yaml,
         squashfs-tools,
         sudo,
         wget,
         xz-utils,
         ${misc:Depends},
         ${python3:Depends}

From this list;

- bzr, git and mercurial should be dynamically installed when using the helper.
- The need for dpkg-dev should be reassessed
- The need for wget should be reassessed.
- The need for xz-utils should be reassessed

These are the build dependencies

Build-Depends: bzr,
               cmake,
               debhelper (>= 9),
               dh-python,
               python3 (>= 3.4),
               python3-apt,
               python3-docopt,
               python3-fixtures,
               python3-jsonschema,
               python3-lxml,
               python3-pkg-resources,
               python3-requests,
               python3-requests-oauthlib,
               python3-setuptools,
               python3-ssoclient,
               python3-testscenarios,
               python3-xdg,
               python3-yaml,
               wget,
               xz-utils

From this list;

- we probably don't need cmake here
- we probably don't need xz-utils or wget if not needed in depends either.