A working Cluster Examples that doesn't use LXC. Smaller snap.

[sklassen]

Overview

This uses a new snap feature that allows for parallel snap so you can create a cluster
on a single machine.

https://snapcraft.io/blog/parallel-installs-test-and-run-multiple-instances-of-snaps

I also separated out the packages into build and stage. (I believe I have split them
correctly)

I added 'snap set couchdb port=xxxx' to ease the installation for the cluster example

Testing recommendations

Compiled and tested on couchdb-sklassen first

Checklist

• [X ] Code is written and works correctly;
• [X ] Changes are covered by tests;
• [X ] Documentation reflects the changes;

[wohali]

Released as version 8:

$ snapcraft status couchdb
Track    Arch    Channel    Version    Revision
2.x      amd64   stable     2.3.1      5
                 candidate  ^          ^
                 beta       ^          ^
                 edge       ^          ^
3.x      amd64   stable     3.0.0      8
                 candidate  ^          ^
                 beta       ^          ^
                 edge       ^          ^
latest   amd64   stable     2.3.1      5
                 candidate  3.0.0      8
                 beta       ^          ^
                 edge       ^          ^