* Verify that acme-tiny is present
* Use run_command rather than subprocess for acme-tiny
Besides consistency with the rest of the code base, this also
add 2 bug fixes:
- ansible should no longer show "warning, junk after json" when using the module
- it also verify the return code of acme-tiny, and so fail when the
verification fail. The previous code didn't check rc, so it would continue
with a empty file