Support fixed version or user provided openthread source to make cirque behavior stable

[erjiaqing]

cirque/dependency_modules.sh

Lines 28 to 40 in bc42efe

	function install_openthread() {
	if [ ! -d "${OPEN_THREAD_DIR}" ]; then
	wget https://github.com/openthread/openthread/archive/master.zip
	unzip master.zip
	rm master.zip
	mv openthread-master openthread
	fi
	pushd .
	cd openthread
	./bootstrap
	make -f examples/Makefile-simulation
	popd
	}

Currently, cirque always download openthread's master code, which is not stable since change in openthread will break cirque.

There are two ways that can make this better,

1. Use a fixed openthread commit id and update it regularly,
2. Allow user specify the path of openthread and use it here