pytests: add basic test for the status led

pytests/test_status_led.py

+from . import boardtype
+
+import os
+import pytest
+
+
+@pytest.mark.skipif(not boardtype.is_librem5(), reason="Not a phone")
+def test_status_led_exists():
+    assert(os.path.exists('/sys/class/leds/red:status/brightness'))
+    assert(os.path.exists('/sys/class/leds/green:status/brightness'))
+    assert(os.path.exists('/sys/class/leds/blue:status/brightness'))