Investigate store-and-reraise exception pattern

[vxgmichel]

In BackendAuthenticatedConn._acquire_transport, a previously-caught exception might be re-raised:

parsec-cloud/parsec/core/backend_connection/authenticated.py

Line 260 in bc179e8

raise self.status_exc

This can lead to traceback issues as shown in this very long trace:
https://sentry.io/organizations/scille/issues/1815651121/events/65fcd73102d8457d9bf678448be9df22/?project=1212848

Here's a way to reproduce the problem (credit goes to @touilleMan)

Python 3.6.9 (default, Nov  7 2019, 10:44:02)
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> exc = None
>>> def foo(exc):
...   raise exc
...
>>> def bar(exc):
...   foo(exc)
...
>>> bar(RuntimeError("1"))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in bar
  File "<stdin>", line 2, in foo
RuntimeError: 1
>>> try:
...   bar(RuntimeError("2"))
... except BaseException as _exc:
...   exc = _exc
...
>>> exc
RuntimeError('2',)
>>> bar(exc)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in bar
  File "<stdin>", line 2, in foo
  File "<stdin>", line 2, in <module>
  File "<stdin>", line 2, in bar
  File "<stdin>", line 2, in foo
RuntimeError: 2
>>> bar(exc)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in bar
  File "<stdin>", line 2, in foo
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in bar
  File "<stdin>", line 2, in foo
  File "<stdin>", line 2, in <module>
  File "<stdin>", line 2, in bar
  File "<stdin>", line 2, in foo
RuntimeError: 2
>>> bar(exc)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in bar
  File "<stdin>", line 2, in foo
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in bar
  File "<stdin>", line 2, in foo
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in bar
  File "<stdin>", line 2, in foo
  File "<stdin>", line 2, in <module>
  File "<stdin>", line 2, in bar
  File "<stdin>", line 2, in foo
RuntimeError: 2
>>> bar(exc)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in bar
  File "<stdin>", line 2, in foo
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in bar
  File "<stdin>", line 2, in foo
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in bar
  File "<stdin>", line 2, in foo
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in bar
  File "<stdin>", line 2, in foo
  File "<stdin>", line 2, in <module>
  File "<stdin>", line 2, in bar
  File "<stdin>", line 2, in foo
RuntimeError: 2
>>>