use `registercloudguest` where available and rework PAYG workaround

[yeoldegrove]

From https://www.suse.com/c/byos-instances-and-the-suse-public-cloud-update-infrastructure/:

For BYOS images with a datestamp later than 20220103, spare -chost- images, the cloud-regionsrv-client package will be installed by default to make registration more straight forward. Unlike for on-demand instances the registration is not automatic on instance startup. The reason for this is that your SUSE registration code is required for access to the update infrastructure.

This means, that never public cloud images in azure/aws/gcp should use registercloudguest to connect to the update servers.

This PR introduces:

• use registercloudguest if it available (baked into the image)
• update old workaround that is broken with new registercloudguest releases
  • fixes #812

tested with the following images

azure

os_image = "SUSE:sles-sap-15-sp3-byos:gen2:2021.12.19"
os_image = "SUSE:sles-sap-15-sp3-byos:gen2:2022.01.27"
os_image = "SUSE:sles-sap-12-sp5-byos:gen2:2021.12.09"
os_image = "SUSE:sles-sap-12-sp5-byos:gen2:2022.01.27"

os_image = "SUSE:sles-sap-15-sp3:gen2:2021.12.19"
os_image = "SUSE:sles-sap-15-sp3:gen2:2022.01.26"
os_image = "SUSE:sles-sap-12-sp5:gen2:2021.12.15"
os_image = "SUSE:sles-sap-12-sp5:gen2:2022.01.26"

GCP

os_image = "suse-byos-cloud/sles-15-sp3-sap-byos-v20211113"
os_image = "suse-byos-cloud/sles-15-sp3-sap-byos-v20220126"
os_image = "suse-byos-cloud/sles-15-sp2-sap-byos-v20220126"
os_image = "suse-byos-cloud/sles-12-sp5-sap-byos-v20220126"

os_image = "suse-sap-cloud/sles-15-sp3-sap-v20211113"
os_image = "suse-sap-cloud/sles-15-sp3-sap-v20220126"
os_image = "suse-sap-cloud/sles-15-sp2-sap-v20220126"
os_image = "suse-sap-cloud/sles-12-sp5-sap-v20220126"

PR for master is #816