usertools: fix telemetry client with python 3

usertools: fix telemetry client with python 3

The client script for use with the telemetry library did not support
Python3, as the data being sent over the socket was in string format.
Python3 requires the data be explicitly converted to bytes before being
sent. Similarly, the received bytes need to be decoded into string
format.

Fixes: 53f293c9a783 ("usertools: replace unsafe input function")
Fixes: fe35622659ed ("usertools: fix telemetry client with python 3")
Fixes: d1b94da4a4e0 ("usertools: add client script for telemetry")
Fixes: 4080e46c8078 ("telemetry: support global metrics")
Cc: stable@dpdk.org
Signed-off-by: Ciara Power <ciara.power@intel.com>
Reviewed-by: Robin Jarry <robin.jarry@6wind.com>
Acked-by: Kevin Laatz <kevin.laatz@intel.com>