node-proxy: catch RequestException in reporter

node-proxy: catch RequestException in reporter

This catches the requests.exceptions.RequestException
exception in the reporter agent so we can better handle the
case where it can't reach the endpoint when trying to send the
collected data.
Before this change, if for some reason the refreshed data couldn't be
sent to the endpoint, it wouldn't have retried because
`self.system.previous_data` was overwritten anyway.

Signed-off-by: Guillaume Abrioux <gabrioux@ibm.com>