Update Android junit docs to make it clear how to specify out path.

docs/android_test_instructions.md

 # Android Test Instructions
 
 [TOC]
 
 ## Device Setup
 
 ### Physical Device Setup
 
 #### ADB Debugging
 
@@ skipping 188 matching lines @@
 for example, `content_junit_tests` and `chrome_junit_tests`.
 
 When adding a new JUnit test, the associated `BUILD.gn` file must be updated.
 For example, adding a test to `chrome_junit_tests` requires to update
 `chrome/android/BUILD.gn`. If you are a GYP user, you will not need to do that
 step in order to run the test locally but it is still required for GN users to
 run the test.
 
 ```shell
 # Build the test suite.
-ninja -C out/Release chrome_junit_tests
+ninja -C out/my_build chrome_junit_tests
 
 # Run the test suite.
-build/android/test_runner.py junit -s chrome_junit_tests --release -vvv
+BUILDTYPE=my_build build/android/test_runner.py junit -s chrome_junit_tests -vvv
 
 # Run a subset of tests. You might need to pass the package name for some tests.
-build/android/test_runner.py junit -s chrome_junit_tests --release -vvv
+BUILDTYPE=my_build build/android/test_runner.py junit -s chrome_junit_tests -vvv
 -f "org.chromium.chrome.browser.media.*"
 ```
 
 ## Gtests
 
 ```shell
 # Build a test suite
 ninja -C out/Release content_unittests
 
 # Run a test suite
@@ skipping 80 matching lines @@
 
 See [Layout Tests](testing/layout_tests.md).
 
 ## Running GPU tests
 
 (e.g. the "Android Debug (Nexus 7)" bot on the chromium.gpu waterfall)
 
 See https://www.chromium.org/developers/testing/gpu-testing for details. Use
 `--browser=android-content-shell`. Examine the stdio from the test invocation on
 the bots to see arguments to pass to `src/content/test/gpu/run_gpu_test.py`.