Improve exception reports when exception can't be reconstructed

Artiq assumes that all exceptions raised by the kernel can be constructed with
a single string argument. This isn't always the case. Especially for
exceptions that originated in python and were propagated to the kernel over
rpc.

With out this change a mosek solver failure looks like:
```
ERROR    root:logging_tools.py:41 Terminating with exception (TypeError: __init__() missing 1 required positional argument: 'msg')
Traceback (most recent call last):
  File "/home/mb/.cache/pypoetry/virtualenvs/ion-transport-1-b41LI0-py3.8/lib/python3.8/site-packages/artiq/master/worker_impl.py", line 540, in main
    exp_inst.run()
  File "/home/mb/.cache/pypoetry/virtualenvs/ion-transport-1-b41LI0-py3.8/lib/python3.8/site-packages/artiq/test_tools/experiment.py", line 82, in wrapper
    meth()
  File "/home/mb/.cache/pypoetry/virtualenvs/ion-transport-1-b41LI0-py3.8/lib/python3.8/site-packages/artiq/language/core.py", line 54, in run_on_core
    return getattr(self, arg).run(run_on_core, ((self,) + k_args), k_kwargs)
  File "/home/mb/.cache/pypoetry/virtualenvs/ion-transport-1-b41LI0-py3.8/lib/python3.8/site-packages/artiq/coredevice/core.py", line 152, in run
    self.comm.serve(embedding_map, symbolizer, demangler)
  File "/home/mb/.cache/pypoetry/virtualenvs/ion-transport-1-b41LI0-py3.8/lib/python3.8/site-packages/artiq/coredevice/comm_kernel.py", line 720, in serve
    self._serve_exception(embedding_map, symbolizer, demangler)
  File "/home/mb/.cache/pypoetry/virtualenvs/ion-transport-1-b41LI0-py3.8/lib/python3.8/site-packages/artiq/coredevice/comm_kernel.py", line 699, in _serve_exception
    python_exn = python_exn_type(
TypeError: __init__() missing 1 required positional argument: 'msg'
```

With this change we get:
```
ERROR    root:logging_tools.py:41 Terminating with exception (RuntimeError: Exception type=<class 'mosek.Error'>, which couldn't be reconstructed (__init__() missing 1 required positional argument: 'msg'))
Core Device Traceback:
Traceback (most recent call first):
  File "/home/mb/oxionics/ion-transport/tests/test_end_to_end.py", line 280, in get_transport
    return self.seq.solve()
  File "/home/mb/oxionics/ion-transport/tests/test_end_to_end.py", line 288, in artiq_worker_test_end_to_end.TransportTestScan.run(..., ...) (RA=+0x2e4)
    self.seq.record(self.get_transport(1e-6 + 1e-7 * x))
mosek.Error(27): rescode.err_license_expired(1001): The license has expired.

End of Core Device Traceback
Traceback (most recent call last):
  File "/home/mb/oxionics/artiq/artiq/master/worker_impl.py", line 540, in main
    exp_inst.run()
  File "/home/mb/oxionics/artiq/artiq/test_tools/experiment.py", line 82, in wrapper
    meth()
  File "/home/mb/oxionics/artiq/artiq/language/core.py", line 54, in run_on_core
    return getattr(self, arg).run(run_on_core, ((self,) + k_args), k_kwargs)
  File "/home/mb/oxionics/artiq/artiq/coredevice/core.py", line 152, in run
    self.comm.serve(embedding_map, symbolizer, demangler)
  File "/home/mb/oxionics/artiq/artiq/coredevice/comm_kernel.py", line 732, in serve
    self._serve_exception(embedding_map, symbolizer, demangler)
  File "/home/mb/oxionics/artiq/artiq/coredevice/comm_kernel.py", line 714, in _serve_exception
    raise python_exn
RuntimeError: Exception type=<class 'mosek.Error'>, which couldn't be reconstructed (__init__() missing 1 required positional argument: 'msg')
```

Signed-off-by: Michael Birtwell <michael.birtwell@oxionics.com>

artiq/coredevice/comm_kernel.py

@@ -686,8 +686,14 @@ class CommKernel:
         else:
             python_exn_type = embedding_map.retrieve_object(core_exn.id)
 
-        python_exn = python_exn_type(
+        try:
-            nested_exceptions[-1][1].format(*nested_exceptions[0][2]))
+            python_exn = python_exn_type(
+                nested_exceptions[-1][1].format(*nested_exceptions[0][2]))
+        except Exception as ex:
+            python_exn = RuntimeError(
+                f"Exception type={python_exn_type}, which couldn't be "
+                f"reconstructed ({ex})"
+            )
         python_exn.artiq_core_exception = core_exn
         raise python_exn