TestAndroidOutput fails to read logcat on ARM64 emulator, API levels 21-22

[mhsmith]

Logs:

13:00:20.733 Thread-176       W  type=1400 audit(0.0:17): avc: denied { execute } for name="logcat" dev="vda" ino=273 scontext=u:r:untrusted_app:s0 tcontext=u:object_r:logcat_exec:s0 tclass=file permissive=0
...
13:00:22.291 python.stderr    W  ERROR: test_bytes (chaquopy.test.android.test_stream.TestAndroidOutput)
13:00:22.291 python.stderr    W  ----------------------------------------------------------------------
13:00:22.292 python.stderr    W  Traceback (most recent call last):
13:00:22.292 python.stderr    W    File "/data/data/com.chaquo.python.demo3/files/chaquopy/AssetFinder/app/chaquopy/test/android/test_stream.py", line 23, in setUp
13:00:22.292 python.stderr    W      self.logcat_process = subprocess.Popen(
13:00:22.292 python.stderr    W    File "stdlib/subprocess.py", line 858, in __init__
13:00:22.292 python.stderr    W    File "stdlib/subprocess.py", line 1704, in _execute_child
13:00:22.292 python.stderr    W  PermissionError: [Errno 13] Permission denied: 'logcat'

It works fine on x86 and x86_64 with API level 21, and on ARM64 with API level 23 and higher.

Since this is apparently a bug in the emulator's SELinux configuration, and there's no other way for an app to read its own logs, we won't be able to fix this issue. But I'll leave it open for visibility for as long as we support these API levels.

[mhsmith]

We will desupport these API levels in the next version of Chaquopy (#718).