Check existence of files and package descriptors before pushing to tng-cat

[mpeuster]

Will allow us to stop early if artifacts vendor.name.version are there already.

curl -H "Content-type:application/json" http://pre-int-sp-ath.5gtango.eu:4011/api/v2/packages?name=asdas&vendor=asdasd&version=0.1

[panstav1]

Highly correlated with this issue of the tng-cat

[mpeuster]

see discussion in: https://gitter.im/mpeuster/tng-package-cat-integration