[lldb] Improve TestAppleSimulatorOSType.py error message

[JDevlieghere]

Summary

Show a more informative error message when we fail to parse the simctl output. It was inspired by https://reviews.llvm.org/D109336 which got reverted because we didn't want to fail silently.

lldb/test/API/tools/lldb-server/TestAppleSimulatorOSType.py

class TestAppleSimulatorOSType(gdbremote_testcase.GdbRemoteTestCaseBase):
 
     mydir = TestBase.compute_mydir(__file__)
 
     # Number of stderr lines to read from the simctl output.
     READ_LINES = 10
 
     def check_simulator_ostype(self, sdk, platform_name, arch=platform.machine()):
         cmd = ['xcrun', 'simctl', 'list', '-j', 'devices']
-        self.trace(' '.join(cmd))
+        cmd_str = ' '.join(cmd)
+        self.trace(cmd_str)
         sim_devices_str = subprocess.check_output(cmd).decode("utf-8")
+        try:
             sim_devices = json.loads(sim_devices_str)['devices']
+        except json.decoder.JSONDecodeError:
+            self.fail("Could not parse '{}' output. Authorization denied?".format(cmd_str))
         # Find an available simulator for the requested platform
         deviceUDID = None
         deviceRuntime = None
         for simulator in sim_devices:
             if isinstance(simulator,dict):
                 runtime = simulator['name']
                 devices = simulator['devices']
             else: