Ticket27135 store obs bw

also:
* fix missing avg bw after moving functions to methods
* add more attrs to V3BWLine that are going to be used by other
  scaling methods

instead of conf and args, so that it's easier to test the method
without creating ConfigParser and ArgumentParser objects.

1. magic methods
2. classmethods
3. staticmethods
4. properties
5. methods

1. magic methods
2. classmethods
3. staticmethods
4. properties
5. methods

1. magic methods
2. classmethods
3. staticmethods
4. properties
5. methods

Ticket27512 warn disk followup

It will only be shown when running sbws without arguments.

since some systems might not allow it.

since some systems might not allow it.

trac: finishes #26937