samples: fix test case status code check

If a driver returns NotImplemented, the status code won't be 404 but the
test should not fail. Use the status argument in get_json for that check.

Change-Id: I71f21589d3a9fa917746e5eecb20f0e883cab830
Improve help strings

Follow oslo.config style guide for help strings better to create
consistent help strings:
* Capitalize first word of each help string
* Finish help strings with "."
* Improve wording

Change-Id: I4723ad672c30146869254695ba82678b082efd91
Merge "samples: fix test case status code check"
Merge "Improve help strings"