Rename API endpoints to better names.

[vpetersson]

We're using some really poorly named api end-points right now, including:

• /api/v0.2/creds
• /api/v0.2/dev-md

Here's what's wrong with them:

• They're not descriptive (you can't figure out what they are for)
• There is no need to abbreviate these URLs (as it only makes them less readable)

Better names would have been

• /api/v0.2/credentials
• /api/v0.2/device-metadata

Since we already use versioning, we need to bump that up before renaming.