Move reusable parts of the AsciiArmoredDetachedSigningService into the parent class
While working on the AptReleaseSigningService for Debian (https://github.com/pulp/pulp_deb/pull/160)
I noticed that the only thing that really needs to be different for each siginig service is the verification of the external script.
As such, most of everything else can be moved into the SigningService parent class, to be reusable across different signing services.
I have started working on the refactor here: https://github.com/pulp/pulpcore/pull/584