fn: I/O related improvements (#809)

*) I/O protocol parse issues should shutdown the container as the container
goes to inconsistent state between calls. (eg. next call may receive previous
calls left overs.)
*) Move ghost read/write code into io_utils in common.
*) Clean unused error from docker Wait()
*) We can catch one case in JSON, if there's remaining unparsed data in
decoder buffer, we can shut the container
*) stdout/stderr when container is not handling a request are now blocked if freezer is also enabled.
*) if a fatal err is set for slot, we do not requeue it and proceed to shutdown
*) added a test function for a few cases with freezer strict behavior

api/agent/protocol/factory.go

@@ -13,6 +13,8 @@ import (
 
 var errInvalidProtocol = errors.New("Invalid Protocol")
 
+var ErrExcessData = errors.New("Excess data in stream")
+
 type errorProto struct {
 	error
 }