The textfile collector will now provide a unified metric description
(that will look like "Metric read from file/a.prom, file/b.prom")
for metrics collected accross several text-files that don't already
have a description.
Also change the error handling in the textfile collector tests to
ContinueOnError to better mirror the real-life use-case.
Signed-off-by: Guillaume Espanel <guillaume.espanel.ext@ovhcloud.com>
Signed-off-by: Guillaume Espanel <guillaume.espanel.ext@ovhcloud.com>
