Vault secret backend

[vnzongzna]

Fixes issue #105

Proposed Changes

• Added Vault as a secret backend for kv/kv-v2 secret engine
• Add Tests

[vnzongzna]

@adrianchifor @ramaro review required

[ramaro]

@vaibhavk any plan on fixing the items we've reviewed?

[prakashrj]

@ramaro. Can you please review these new updates?

[uberspot]

I tested this PR locally btw and no regression popped up.
Two "nice to have"s remain:

• Use target_name from the inventory in the vault class instead of changing the RefBackend constructor (@ramaro might have a tip for that)
• Test vaultkv properly in the CI/CD since now the vaultkv: secret isn't in the examples/ so tests don't run on it in Travis.

Other than that the PR looks good.
I'll approve but ideally would like a second approval from @ramaro or @adrianchifor before merging. :)

[ramaro]

just 2 nitpicks and I think we're good to merge!
Let's also add some docs (other than the kap) after.

[vnzongzna]

I'll add the vaultkv information on docs by making a new PR for gh-pages branch

[uberspot]

I'll add the vaultkv information on docs by making a new PR for gh-pages branch

That won't work unfortunately because of permissions. Ideally if you update the docs under docs/ on the master branch I can easily update the gh-pages part. :)