Expand `policy list_roles` and `policy list_atoms` with more filters

[pederhan]

It would be nice to be able to search for roles and atoms using more filters than just name. We could support searching for things like descriptions, atom members and hosts they are applied to.

New options

policy list_roles

• -description: List roles with the given description
• -atom: List roles containing the given atom
• -host: List roles applied to the given host (Maybe? host info already lists roles, but only the names!)

policy list_atoms

• -description: List atoms with a given description
• -host: List atoms applied to the given host through its roles

Examples

Find all roles with a description containing the phrase web:

policy list_roles * -description *web*

Find all roles with the atom is_web_server

policy list_roles * -atom is_web_server

Find all atoms applied to a host through its roles:

policy list_atoms * -host host1.example.com

Suggestion: Make the FILTER argument optional

> policy list_roles --help
usage: mreg-cli policy list_roles [-h] FILTER

List all roles by given filters

positional arguments:
  FILTER      Role name, or part of name. You can use * as a wildcard.

options:
  -h, --help  show this help message and exit

It could be a good idea to make the positional FILTER argument optional if a positional argument is provided, since it's likely that one primarily wants to search through all roles when narrowing down by things such as atom members.

I.e.

policy list_roles -atom is_web_server

However, we should still support having a filter if they user wants to narrow it down by name in addition to members:

policy list_roles *foo* -atom is_web_server

Disclaimer

I am aware the name and description filtering functionality is largely achievable with policy list_{roles,atoms} * | <regex>, but that does not differentiate between name and description, and it has limited filtering potential beyond that.