samples: lsm6dsl: Add a harness_config

In order to enable sample to be run and evaluated in sanitycheck,
add a harness_config to validate sample output:
- Add "regex" to match on sample output
- Add "timeout" to save some time when debugging
- Add "ordered" instruction. Since sample is running a while loop
test verdict can potentially be computed on previous run output,
issuing a wrong status.

Last, since sanitycheck regex does not play well them, rework
sample to output without parenthesis.

Tested on disco_l475_iot1

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>