chore(android): auto-download NDK r21c for module builds if needed

[jquick-axway]

JIRA:

• https://jira.appcelerator.org/browse/TIMOB-27939
• https://jira.appcelerator.org/browse/TIMOB-27776

Summary:

• The macOS distribution of Android NDK r21c has been "notarized" by Google. This means macOS Catalina will no longer show security popups when attempting to do a module build.
• Will only auto-download this NDK version for module builds if no installation was found.
• Fixed builds with NDK r21 to no longer log harmless "Bad file descriptor" errors.

Module Test:

1. Use a macOS Catalina machine that does not have the NDK installed.
2. Download the zipped source of module ti.imagefactory.
3. Open the Terminal.
4. CD to directory: ./ti.imagefactory/android
5. Enter: appc run -p android
6. Verify that you see log message similar to the below. This may take a few minutes.
   [INFO] [GRADLE] Preparing "Install NDK (revision: 21.2.6472646)"
7. Verify that the module builds and its example project runs.

[build]

	Messages
📖	💾 Here's the generated SDK zipfile.
📖	✊ The commits in this PR match our conventions! Feel free to Rebase and Merge this PR when ready.
📖	✅ All tests are passing Nice one! All 6631 tests are passing. (There are 703 skipped tests not included in that total)

Generated by 🚫 dangerJS against 5ecb06b

[garymathews]

CR: PASS

[ssjsamir]

FR Passed: No longer see Bad file descriptor errors and able to install NDK if no other NDKs are found.

Test Environment

MacOS Catalina: 10.15.5 Beta
Xcode: 11.4
Java Version: 1.8.0_131
Android NDK: 21.1.6273396-beta2
Node.js: 10.16.3
""NPM":"5.0.0","CLI":"8.0.0""
Andoird Pixl xl 7.1.1 Emulator