Create `dummygatekeeper` for 5GTANGO packages

[mpeuster]

Copy SONATA DK and adopt it to support 5GTANGO example package.

Dev branch 5gtango/dev (https://github.com/mpeuster/son-emu/tree/5gtango/dev).

Rename it? Dummygatekeeper is a strange name. What about tango/llcm for 'lightweight lifecycle manager'?

• [x] copy seed code (api/tango/llcm.py)
• [x] fix style check (flake8 --exclude=.eggs,devops --ignore=E501 .)
• [x] create example topology (tango_default_cli_topology_2_pop.py)
• [x] create a example package (where?) w. service and 2x ubuntu:trusty VNF (put to misc/)
• [x] update code to allow on-boarding of the 5GTANGO example package
• [x] update code to allow simple instantiation of the 5GTANGO example package
• [x] unittests
• [x] update example1 and example2 in wiki
• [x] document new feature in a release draft to keep track
• [x] push to OSM
• [x] merge code to OSM repo (https://osm.etsi.org/gerrit/#/c/6407/)
• [x] sync OSM master with github

ATTENTION: Do all changes within one commit (--amend to update) to be compatible to OSM's Gerrit-based code review.

git commit --amend
git push --force

Demo package tree:

/tmp/son-dummy-gk/catalog/services/5159e447-8834-45dc-8396-e292e445816a
├── Definitions
│   ├── tango_default-vnf0.yml
│   ├── tango_default-vnf1.yml
│   └── tango_emulator_example.yml
├── etsi_manifest.mf
└── TOSCA-Metadata
    ├── NAPD.yaml
    └── TOSCA.meta

On-board:

curl -i -X POST -F package=@misc/eu.5gtango.emulator-example-service.0.1.tgo http://127.0.0.1:5000/packages

Instantiate:

curl -X POST http://127.0.0.1:5000/instantiations -d "{}"