digest auth does not honor load balancer cookie based sticky sessions

[moserke]

trafficstars

For load balancers that do cookie based sessions for stickiness, digest auth does not set the "Set-Cookie" received from the setup of digest and on the second request once digest is set up you are not guaranteed to be sent to the same back end node.

setup digest auth should look for Set-Cookie in the response and add them to the subsequent HTTP calls.

[jnunemaker]

Related to #313