Shard android_ndk_integration_test.

Before this CL with --runs_per_test=10 on 2015 Macbook Pro

INFO: Elapsed time: 622.222s, Critical Path: 314.33s
//src/test/shell/bazel/android:android_ndk_integration_test             TIMEOUT in 10 out of 10 in 314.3s
  Stats over 10 runs: max = 314.3s, min = 306.1s, avg = 308.9s, dev = 3.5s

After this CL with --runs_per_test=10 on 2015 Macbook Pro

INFO: Elapsed time: 875.356s, Critical Path: 148.11s
//src/test/shell/bazel/android:android_ndk_integration_test              PASSED in 148.1s
  Stats over 60 runs: max = 148.1s, min = 25.3s, avg = 70.2s, dev = 38.7s

RELNOTES: None
PiperOrigin-RevId: 177048666

src/test/shell/bazel/android/BUILD

@@ -77,6 +77,7 @@ sh_test(
         "//external:android_sdk_for_testing",
         "//src/test/shell/bazel:test-deps",
     ],
+    shard_count = 6,
 )
 
 sh_test(