This update for python-rtslib-fb fixes the following issues:

- Update to version v2.1.73 (bsc#1173257 CVE-2020-14019):
* version 2.1.73
* save_to_file: fix fd open mode
* saveconfig: copy temp configfile with permissions
* saveconfig: open the temp configfile with modes set
* Fix "is not" with a literal SyntaxWarning
* Fix an incorrect config path in two comments
* version 2.1.72
* Do not change dbroot after drivers have been registered
* Remove '_if_needed' from RTSRoot._set_dbroot()'s name
Replacing old tarball with python-rtslib-fb-v2.1.73.tar.xz

This update was imported from the SUSE:SLE-15-SP2:Update update project.