kata builtin proxy has always watched the qemu's console
whether proxy's debug is set or not, this is not aligned
with kata cli. This patch will change it and watch the
qemu's console only when proxy's debug is set in kata config.
Fixes: #1318
Signed-off-by: fupan <lifupan@gmail.com>
Callers can use setProxy to ask agent to use an existing proxy.
agent is modified to rely on its state.URL to tell if an
its proxy is a valid one. And startProxy will skip a valid
proxy since it is already started.
Signed-off-by: Peng Tao <bergwolf@gmail.com>