Make uwsgi app to not demonize

Make uwsgi app to not demonize

Supervisord doesn't support demonize applications, thus we have to
make the uwsgi application to run not in background.

- Fixed Yardstick API path.
- Fixed HttpClient class to raise correct exception when
  the HTML response (not JSON) like 4xx, 5xx is received.
  (http://docs.python-requests.org/en/master/user/quickstart/#json-response-content)

JIRA: YARDSTICK-1297

Change-Id: I4d1c1bb7266eeed0bd357bd28b91206d1580611f
Signed-off-by: Mytnyk, Volodymyr <volodymyrx.mytnyk@intel.com>