[login_manager] Enable parallel offline/online login
[login_manager] Enable parallel offline/online login

Replace obsolete --in-chrome-auth flag with new --parallel-auth flag

BUG=chromium-os:4929
TEST=unit tests in chrome, run all login_* autotests

Change-Id: I54d35ba8e2467288bd1eec1fb12a6cb1dc23af84

Review URL: http://codereview.chromium.org/3578020

joshfire/chromiumos-platform-login_manager,chadversary/chromiumos.platform.login_manager,joshfire/chromiumos-platform-login_manager,chadversary/chromiumos.platform.login_manager,joshfire/chromiumos-platform-login_manager,chadversary/chromiumos.platform.login_manager