Correctly handle HttpError during authentication (SOC-3456)
Correctly handle HttpError during authentication (SOC-3456)

- 503 status code will not be caught on production systems, and
  requires capturing a different exception

Change-Id: Ice10d449452db7b8660f95912589eb5f40cde903

ArdanaCLM/ardana-service,ArdanaCLM/ardana-service