Add support to override keyring in aptly mirror create command

[mdechiaro]

Affected Puppet, Ruby, OS and module versions/distributions

• Puppet: N/A
• Ruby: N/A
• Distribution: N/A
• Module version: 2.1.0

How to reproduce (e.g Puppet code you use)

N/A

What are you seeing

The keyring parameter is available as a class parameter, but it isn't exposed in the aptly mirror create command, so it cannot be used to set custom location of keys. When this flag is absent, then the default location according to the docs is in ~/.gnupg/trustedkeys.gpg.

What behaviour did you expect instead

The ability to override keyring in aptly mirror create command.

Output log

Any additional information you'd like to impart

[jay7x]

Hi @mdechiaro! I see you made the change in your branch, but you did no PR here. Feel free to raise a PR.