print all debug msg from clients when using debug flag

Most of python-*clients would print request url and response body when
the logger is set in debug mode, but novaclient and cinderclient not.
They need another switch "http_log_debug". Adding
"http_log_debug=CONF.debug" could help rally prints all debug messages
from clients when using debug flag.

Change-Id: I503c3e359702227e45d72c1bfe8dd88359b18b5c
Merge "print all debug msg from clients when using debug flag"