Make parsing of results in WeavePing.py harness more robust
Make parsing of results in WeavePing.py harness more robust

Improve the parsing.  When running the tests in the presence of
faults, sometimes the last line that contained an `(` and a `%`
characters did not contain a valid packet loss.  This change fixes the
parsing, and makes it impervious to `ValueError` resulting from the
conversion to float.

openweave/openweave-core,openweave/openweave-core,openweave/openweave-core,openweave/openweave-core,openweave/openweave-core,openweave/openweave-core