Fix devserver to unpack rootfs and serve it.
Fix devserver to unpack rootfs and serve it.

Review URL: http://codereview.chromium.org/1604014

mgireesh05/dev-util,marineam/coreos-dev-util,coreos/dev-util,marineam/coreos-dev-util,mgireesh05/dev-util,coreos/dev-util,coreos/dev-util,mgireesh05/dev-util