Fix the Admin API endpoints when it response with a client error
response code.
The most of the client response error send a JSON body but the
`Content-Type` header wasn't set to the appropriated value. This commit
fixes them and it adds assertions to the tests to very the
`Content-Type` header.
Updates the README to briefly document about the format of the client
errors endpoints responses.
Change-Id: Ifaf2122def801701211438ce241046be1adc0e8c
Rename the entities in the endpoint paths from singular after we have
agreed that it matches with API design best practices.
Change-Id: I5bdc086c64c6f93e45a13436b65863fc3e8d864e
This change allows the creation and deletion of api keys via the admin API.
It adds two methods for deletion, one via the name and projectID and the
second one via the serialized apikey directly.
Change-Id: Ida8aa729e716db58c671a901e5f7e39253e89a0d
