Host handler authentication unit tests (#9)

Adding tests to cover the authentication and authorization aspects of
the hosts API, and with that, we complete the scope of unit-tests for
the MVP.

A few issues with the configuration package not properly loading
configuration from environment variables were found while writing the
unit tests and were also fixed.

Signed-off-by: Filipe Utzig <filipe@gringolito.com>

README.md

@@ -23,7 +23,7 @@ server, like:
 - [x] Create .deb deployable package (target at least to armv6)
     - [x] .rpm, .apk, ArchLinux packages and tarball archives for all the main architectures (BONUS)
 - [x] Create a OpenAI/Swagger documentation
-- [ ] Add unit tests
+- [x] Add unit tests
 
 ### Phase-2