Fix IDEUI-221 Better app health check

Note: Commit replayed because erase by newer one (2c8e6d erased by
c80bda).

Enhancements made:
* if HEAD method is not supported, there's a fallback on GET one,
* all 1xx, 2xx and 3xx are now considered as working status code.
Merge pull request #88 from stephanedaviet/IDEUI-221

Fix IDEUI-221 Better app health check