Adding ARM community builder support

[codexlynx]

List of Changes Proposed

Added support for the Arm Packer builder.

Testing Evidence

$ pytest tests/packerlicious/community/test_builder_arm.py
================================================== test session starts ==================================================
platform linux -- Python 3.6.7, pytest-4.1.1, py-1.7.0, pluggy-0.8.1 -- /home/user/packerlicious/venv/bin/python
cachedir: .pytest_cache
rootdir: /home/user/packerlicious, inifile: setup.cfg
collected 1 item                                                                                                        

tests/packerlicious/community/test_builder_arm.py::TestArmBuilder::test_required_fields_missing PASSED            [100%]

=============================================== 1 passed in 0.01 seconds ================================================```

[coveralls]

Coverage remained the same at 100.0% when pulling 7afc599 on codexlynx:feature/add-builder-arm-image-support into 44a4301 on mayn:master.

[mayn]

@codexlynx , thanks for taking the time to add this!

1. I noticed the arm-image builder supports some other parameters in its source, do we want to add those too?
2. few minor name changes, see the suggestions.

[codexlynx]

Hi @coveralls, the renaming is a good idea. Regarding the second point, yes it is true, but the parameters are undocumented. They only have the example templates. For me and my use case is okay. What do you think?

[mayn]

@codexlynx thanks for the feedback. I opened an issue with project maintainers for help adding additional attributes.

[codexlynx]

Thanks you for this project.