Auto merge of #45580 - kennytm:sdkmanager, r=alexcrichton

Auto merge of #45580 - kennytm:sdkmanager, r=alexcrichton

ci: Upgrade Android SDK/NDK and refactor to use sdkmanager/avdmanager.

* SDK tools is upgraded to 27.0.0.

* Stopped using the deprecated `android` tool, instead use the recommended `sdkmanager` and `avdmanager`.

* NDK is upgrade to r15c.

    The r15 series [dropped support for android-9](https://github.com/android-ndk/ndk/wiki/Changelog-r15) (2.3 / Gingerbread), the minimal supported version is now android-14 (4.0 / Ice Cream Sandwich).

r? @alexcrichton

(WIP, haven't confirmed if the change really works yet)