Previously auth_token was initialized once in __init__ method.
After that we stored token in session headers. So to refresh token
users need to instantiate a new session inside http client or
re-create client itself.
In order to provide possibility to refresh token we need
to add token header before sending the request. So users can
just update auth_token attribute in the HTTPClient to refresh
user token.
Change-Id: Ifebe9011870bbddc46fc6d6a26563641d5559e97
Closes-Bug: #1563495
kairat_kushaev
2561e4061c