tests/acceptance: Allow running Orange Pi test using cached artifacts

Unfortunately the Armbian 19.11.3 image has been removed from the
dl.armbian.com file server. Developers having the artifact cached
can still run the test. Allow them to, until we find a proper
solution to share binaries with the whole community.

This avoids (when file manually added to cache):

  BootLinuxConsole.test_arm_orangepi_bionic_19_11: CANCEL: Missing asset https://dl.armbian.com/orangepipc/archive/Armbian_19.11.3_Orangepipc_bionic_current_5.3.9.7z

 (1.06 s)

Reported-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Bin Meng <bin.meng@windriver.com>
Tested-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Reviewed-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Message-Id: <20201023131808.3198005-3-f4bug@amsat.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>

tests/acceptance/boot_linux_console.py

@@ -780,6 +780,8 @@ def test_arm_orangepi_sd(self):
         # Wait for VM to shut down gracefully
         self.vm.wait()
 
+    @skipUnless(os.getenv('ARMBIAN_ARTIFACTS_CACHED'),
+                'Test artifacts fetched from unreliable dl.armbian.com')
     @skipUnless(os.getenv('AVOCADO_ALLOW_LARGE_STORAGE'), 'storage limited')
     @skipUnless(P7ZIP_AVAILABLE, '7z not installed')
     def test_arm_orangepi_bionic(self):