Test Android Testing on 18.04 and reduce emulator flakes (#346)
Test Android Testing on 18.04 and reduce emulator flakes (#346)

* Test Android Testing on 18.04

* Use --spawn_strategy=standalone to reduce flakes

Tested locally.

```
$ bazel test //... --spawn_strategy=standalone

INFO: Elapsed time: 357.294s, Critical Path: 140.44s, Remote (0.00% of the time): [queue: 0.00%, setup: 0.00%, process: 0.00%]
INFO: 1035 processes: 938 local, 97 worker.
INFO: Build completed successfully, 1136 total actions
//ui/espresso/BasicSample:BasicSampleInstrumentationTest_19_x86          PASSED in 45.1s
//ui/espresso/BasicSample:BasicSampleInstrumentationTest_21_x86          PASSED in 55.7s
//ui/espresso/BasicSample:BasicSampleInstrumentationTest_22_x86          PASSED in 60.1s
//ui/espresso/BasicSample:BasicSampleInstrumentationTest_23_x86          PASSED in 57.6s
//ui/espresso/CustomMatcherSample:CustomMatcherSampleInstrumentationTest_19_x86 PASSED in 46.3s
//ui/espresso/CustomMatcherSample:CustomMatcherSampleInstrumentationTest_21_x86 PASSED in 77.4s
//ui/espresso/CustomMatcherSample:CustomMatcherSampleInstrumentationTest_22_x86 PASSED in 68.7s
//ui/espresso/CustomMatcherSample:CustomMatcherSampleInstrumentationTest_23_x86 PASSED in 84.2s
//ui/espresso/DataAdapterSample:DataAdapterSampleInstrumentationTest_19_x86 PASSED in 54.7s
//ui/espresso/DataAdapterSample:DataAdapterSampleInstrumentationTest_21_x86 PASSED in 80.1s
//ui/espresso/DataAdapterSample:DataAdapterSampleInstrumentationTest_22_x86 PASSED in 85.0s
//ui/espresso/DataAdapterSample:DataAdapterSampleInstrumentationTest_23_x86 PASSED in 48.6s
//ui/espresso/IdlingResourceSample:IdlingResourceSampleInstrumentationTest_19_x86 PASSED in 39.4s
//ui/espresso/IdlingResourceSample:IdlingResourceSampleInstrumentationTest_21_x86 PASSED in 56.4s
//ui/espresso/IdlingResourceSample:IdlingResourceSampleInstrumentationTest_22_x86 PASSED in 56.4s
//ui/espresso/IdlingResourceSample:IdlingResourceSampleInstrumentationTest_23_x86 PASSED in 43.9s
//ui/espresso/IntentsAdvancedSample:IntentsAdvancedSampleInstrumentationTest_19_x86 PASSED in 43.2s
//ui/espresso/IntentsAdvancedSample:IntentsAdvancedSampleInstrumentationTest_21_x86 PASSED in 62.1s
//ui/espresso/IntentsAdvancedSample:IntentsAdvancedSampleInstrumentationTest_22_x86 PASSED in 47.1s
//ui/espresso/IntentsAdvancedSample:IntentsAdvancedSampleInstrumentationTest_23_x86 PASSED in 60.2s
//ui/espresso/IntentsBasicSample:IntentsBasicSampleInstrumentationTest_19_x86 PASSED in 55.2s
//ui/espresso/IntentsBasicSample:IntentsBasicSampleInstrumentationTest_21_x86 PASSED in 67.2s
//ui/espresso/IntentsBasicSample:IntentsBasicSampleInstrumentationTest_22_x86 PASSED in 64.9s
//ui/espresso/IntentsBasicSample:IntentsBasicSampleInstrumentationTest_23_x86 PASSED in 66.6s
//ui/espresso/MultiWindowSample:MultiWindowSampleInstrumentationTest_19_x86 PASSED in 54.1s
//ui/espresso/MultiWindowSample:MultiWindowSampleInstrumentationTest_21_x86 PASSED in 78.2s
//ui/espresso/MultiWindowSample:MultiWindowSampleInstrumentationTest_22_x86 PASSED in 76.0s
//ui/espresso/MultiWindowSample:MultiWindowSampleInstrumentationTest_23_x86 PASSED in 81.4s
//ui/espresso/RecyclerViewSample:RecyclerViewSampleInstrumentationTest_19_x86 PASSED in 45.3s
//ui/espresso/RecyclerViewSample:RecyclerViewSampleInstrumentationTest_21_x86 PASSED in 63.7s
//ui/espresso/RecyclerViewSample:RecyclerViewSampleInstrumentationTest_22_x86 PASSED in 54.9s
//ui/espresso/RecyclerViewSample:RecyclerViewSampleInstrumentationTest_23_x86 PASSED in 61.5s
//ui/uiautomator/BasicSample:BasicSampleInstrumentationTest_19_x86       PASSED in 73.3s
//ui/uiautomator/BasicSample:BasicSampleInstrumentationTest_21_x86       PASSED in 62.8s
//ui/uiautomator/BasicSample:BasicSampleInstrumentationTest_22_x86       PASSED in 60.2s
//ui/uiautomator/BasicSample:BasicSampleInstrumentationTest_23_x86       PASSED in 80.2s

INFO: Build completed successfully, 1136 total actions
```

* Only test on emulator-23

bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration