Partially make pychromecast v7.2.0 compatible

[piyueh]

My Linux distribution is now providing pychromecast 7.1.1 and higher. So I made some changes to make mkchromecast works with my setting.

Coverage

1. I only have one Google Home Mini, so I didn't look into video and YouTube streaming. Only checked the audio casting.
2. I don't use the systray. So not sure if the systray works.
3. Tested with both pychromecast 7.2.0 and 7.1.0. Didn't go back further.
4. Tested with Python 3.8.

Changes

Because my use case is very limited, these are small changes. But still, hope this can help some users.

1. improving --reset by adding get_sink_list and modifying remove_sink:
   If mkchromecast crashed due to some reasons, sometimes the sinks it created were still there. Running with --reset would not kill those residual sinks because mkchromecast.pulseaudio._sink_num is None in this situation. So I added get_sink_list to get related sinks and remove them.

2. adding dummy reboot to replace pychromecast.dial.reboot when it does not exist:
   Since Remove reboot function home-assistant-libs/pychromecast#394, pychromecast.dial.reboot does not exist anymore. It seems there's currently no alternative way to reboot a device. But just in case rebooting reappears in the future, I didn't modify the existing code in mkchromecast. I simply added a dummy reboot that is doing nothing.

3. replacing Chromacast.host with Chromecast.socket_client.host:
   Remove host and port from Chromecast object home-assistant-libs/pychromecast#395 removed the host and port attributes under Chromecast objects. But Chromecast.socket_client.host has been a valid attribute since pychromecast v3.0.0. Also, see Chromecast object has None host home-assistant-libs/pychromecast#381 and Report host+port for discovered casts home-assistant-libs/pychromecast#385.

4. fix the return of pychromecast.get_chromecasts():
   Track services based on UUID instead of mDNS service name home-assistant-libs/pychromecast#380 changed the output of pychromecast.get_chromecasts to a tuple. I believe this is the cause of issue pychromecast 7.1.1-1 breaks mkchromecast #322 .