speed measurements fail gracelessly when default executable missing

[jesteria]

🐞 Bug Report

Description

When the default speed-testing executable – i.e. ndt7-client or speedtest – are missing from the measurement execution environment, speed measurements speed-ndt7 and speed-ookla fail with an uncaught exception.

(If the missing executable is specified as an explicit measurement parameter, the measurement catches this and reports the error gracefully.)

The speed measurements' parameter-checking should handle the default value for this parameter as well, such that the behavior is the same.

Steps to Reproduce

On a machine with Netrics v0.0.1 installed but which is missing either underlying test executable, e.g.:

netrics debug run speed-ndt7