python: Fix issue with probes for JSONRPC connections

python: Fix issue with probes for JSONRPC connections

When opening a JSONRPC connection, the health probes
are incorrectly getting turned off for connections
that need probes.

In other words, when stream_or_pstream_needs_probes()
return non-zero, the probes are gettting disabled as
the probe interval is getting set to zero. This leads
to incorrect behavior such that probes are:

  - not getting turned off for unix: connections
  - getting turned off for tcp:/ssl: connections

The changes in this commit fix this issue.

Signed-off-by: Sumit Garg <sumit@extremenetworks.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>