Update account active API to return 204 instead of 404.

Previously, 404 could indicate an account does not exist or an account
in inactive.

Now, 204 indicates the account is valid and inactive Also, the 200
response was updated to return `ok` for clarity and consistency
with the capabilities API.

Change-Id: I39f2fb710cf0cc2417cd727b3a34af97291c683d
2 files changed