[sap-hana] Retention not applied to tenant databases

[poulpreben]

Describe the bug
When using these scripts to quiesce SAP HANA instances, the configured retention is not applied to the tenant database(s). It is only applied to SYSTEMDB. I have an idea how to fix it - will submit PR for further discussion.

To Reproduce
Steps to reproduce the behavior:

1. Configure backup of a HANA 2.0 instance with the pre/post scripts
2. Review present restore points in HANA Studio or VBR after the specified number of days

Expected behavior
It is expected that database backup retention is applied to both SYSTEMDB and the corresponding tenant database(s) on the instance.

System information:

• OS: RHEL 7.6 (Linux 3.10.0-957.e17.x86_64)
• HANA instance version 2.00.045.00.1575639312
• HANA Studio version 2.3.47
• Veeam Backup & Replication 10.0.1

[tsightler]

I had originally worked on this back in March but didn't have a lot of success. I added code to loop through each database but needed to handle permissions and the code just became difficult to follow (even more so than currently) and I was struggling to troubleshoot the errors. At that point I kind of gave up until I had more time to refactor the purge logs section into a function and I didn't think the issue was pressing. Since this has come up multiple times in the last few months I'll take another stab at it over the coming weeks.