ci emulator: Disable animations and other UI/UX features (#198)

* ci emulator: Use Nexus 6 instead of 5X

Should be a tad newer.

* ci emulator: Disable animations and other UI/UX features

We only care about starting a very simple UI-less app for now, and this
seems to fix the deadlock that occurs right about every CI emulator job
just before `adb install` runs.  It hopefully also makes the runs a bit
faster, but this wasn't measured/compared in detail due to already high
runtime variance.

.github/workflows/rust.yml

@@ -115,7 +115,9 @@ jobs:
         arch: x86_64
         # the `googleapis` emulator target is considerably slower on CI.
         target: default
-        profile: Nexus 5X
+        profile: Nexus 6
+        emulator-options: -no-window -gpu swiftshader_indirect -noaudio -no-boot-anim -camera-back none
+        disable-animations: true
         script: ./.github/workflows/android_test.sh "${{ steps.download.outputs.download-path }}"
     - name: Upload emulator logs
       uses: actions/upload-artifact@v2