BigSwitch: Widen range of HTTPExceptions caught

In order to trigger a reconnect, the Big Switch
plugin was only checking for httplib.ImproperConnectionState
which doesn't include relevant exceptions that
indicate a reconnect is necessary. This patch
adjusts it to reconnect on any HTTPException.

Closes-Bug: #1289236
Change-Id: I4b389172dc4a53b0381e40005d8421f71b7d8522
Merge "BigSwitch: Widen range of HTTPExceptions caught"