Eventually
- I’ve downloaded the x86 package where after signing the mentioned verify.jar was not complaining about invalid cert any longer.
- replaced the apk into the armv7l installation (target one)
- check if the verification is working - and it was (when signing with native tool is not)
- encounter the same issue … after the run…
For now I’ve made a hack and modified the
./node-v6.11.4-linux-armv7l/lib/node_modules/appium/node_modules/appium-adb/build/lib/tools/apk-signing.js
so it would return a true even if it looks not signed.
286
287 case 20:
288 context$1$0.prev = 20;
289 context$1$0.t0 = context$1$0’catch’;
290
291 _loggerJs2[‘default’].debug(“App not signed with debug cert.”);
292 return context$1$0.abrupt(‘return’, true);
293
It looks like a bug in https://nodejs.org/dist/v6.11.4/node-v6.11.4-linux-armv7l.tar.xz package during verifying and singing apks.
Could it be fixed please ? 
Regards
Janusz