ISSUE-3127: Python Pulsar client appears to throw regular Exceptions instead of PulsarExceptions

[sijie]

Original Issue: apache#3127

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Expected behavior

The Python client should throw a subclass of Exception, not just Exception.

Actual behavior

An Exception is thrown. See, for example:

In [2]: p = pulsar.Client()

In [3]: c = p.get_consumer("foo")
2018-12-04 17:24:48.860 INFO  ConnectionPool:63 | Created connection for pulsar://localhost:6650
2018-12-04 17:24:48.871 ERROR ClientConnection:329 | [<none> -> pulsar://localhost:6650] Failed to establish connection: Connection refused
2018-12-04 17:24:48.872 INFO  ClientConnection:1237 | [<none> -> pulsar://localhost:6650] Connection closed
2018-12-04 17:24:48.872 ERROR ClientImpl:374 | Error Checking/Getting Partition Metadata while Subscribing- 5
2018-12-04 17:24:48.872 INFO  ClientConnection:195 | [<none> -> pulsar://localhost:6650] Destroyed connection

< deleted internal wrapper code >

Exception: Pulsar error: ConnectError

To demonstrate it's not a subclass:

In [8]: try:
   ...:     c.receive(timeout_millis=500)
   ...: except Exception as e:
   ...:     print(type(e))
   ...:
<class 'Exception'>

Steps to reproduce

Easiest way is probably supply a bogus URL to get a ConnectError

System configuration

Pulsar version: 2.2.0 for both Pulsar and the Python client