docs improvements

[holmanb]

Proposed Commit Message

Improve docs.

- remove unnecessary "First Boot Determination" from tox
- reorder user-data formats based on usage frequency

Additional Context

cloud-config at the top, upstart at the bottom

[holmanb]

[holmanb]

I might have a follow-up PR to add to this, but this PR is ready for review now.

[holmanb]

current usage:

isa~/cloud-init(holmanb/docs|✚1) git grep -L vi: | grep doc | wc -l
75
isa~/cloud-init(holmanb/docs|✚1) git grep -l vi: | grep doc | wc -l
47