Simplify kuksa-client docker build and reducing resulting image size

[SebastianSchildt]

This fixes #682

On a high level

• switch to a glibc build
• this reduced build times as grpc wheels exist
• as a side effect the existing glibc wheels are already small
• using pyinstaller only ship the parts of python necessary to run the client, thus reducing size over using a python base image

This fixes the huge size of the arm image, while at the same time even reducing the amd64 image compared to master

Arm64 size now

ttl.sh/kuksa.val/kuksa-client-ff43b39d56fff605c6330c078dea4b383cade50f        latest                 e2dce0b872fd   About a minute ago   73.1MB

[SebastianSchildt]

I tested secure. lgtm.