Move NegotiatingClientAuthentication creation to ChromotingClient.

For the new SPAKE2 authenticator we need to pass client_jid
to the authenticator. This wasn't possible previously because
NegotiatingClientAuthenticator was created before signaling is
connected. Moved NegotiatingClientAuthentication creation to
ChromotingClient.

BUG=589698

Committed: https://crrev.com/279bf7c76a3e0bfbbd28748d0d02fcead88f4436
Cr-Commit-Position: refs/heads/master@{#380779}

Review URL: https://codereview.chromium.org/1778023002

Cr-Commit-Position: refs/heads/master@{#380831}
12 files changed