FIX eclair-cli error code in case of HTTP problem

Last command of eclair-cli is a curl piped to jq. In case of an
error with the curl command (for instance, eclair service is not
running) the error code was swallowed by the pipe wich will
return the exit code of the last command of the pipe (here, jq).

Setting `pipefail` ensures that the error code of curl is
preserve in case of HTTP issue.

This can come handy, for instance, to check that eclair is not
ok:

```
if eclair-cli getinfo
then
  echo eclair is answering
else
  echo problem communicating with eclair
fi
```

eclair-core/eclair-cli

@@ -166,4 +166,5 @@ else
 fi
 
 # we're now ready to execute the API call
+set -o pipefail # ensures we preserve curl error code in case of HTTP issue
 eval curl "--user $auth --silent --show-error -X POST -H \"Content-Type: application/x-www-form-urlencoded\" $api_payload $api_url/$api_endpoint" | jq -r "$jq_filter"