Hello,

Here is again a change for Borg to allow to give the --umask option on each borg invocation.

Please fetch branch `borg-umask` at `http://git.ni.fr.eu.org/nicolas/propellor.git`.

As a side change, I use `{now}` instead of a call to `$(date …)`, I think it's more idiomatic for borg usage.

Tested with stretch and buster.

> [[merged|done]] thanks for the contribution. --[[Joey]]
