Provide granular noop for ssh configuration (#789)

* Provide granular noop for shh configuration

We would like to have more fine grained options on applying or not specific configurations.

This commit let the user choose to noop some configuration with a few new
boolean variables.

Motivation for theses options are we may configure ourselves some (ssh host key
regeneration in a templating system) or we are not ready for others (ssh_kex
will break dist-upgrades, letting the operator without ssh).

Signed-off-by: seven beep <[email protected]>

* Provide granula noop for ssh configuration

We would like to have more fine grained options on applying or not specific configurations.

This commit let the user choose to disable configurations for `ssh_host_key_config`,
`ssh_ciphers_config`, `ssh_host_key_config`, `ssh_macs_config` by setting them
to False.

Motivation for theses options are we may configure ourselves some (ssh host key
regeneration in a templating system) or we are not ready for others (ssh_kex
will break dist-upgrades, letting the operator without ssh).

Signed-off-by: seven beep <[email protected]>

---------

Signed-off-by: seven beep <[email protected]>

roles/ssh_hardening/meta/argument_specs.yml

@@ -29,7 +29,7 @@ argument_specs:
           Default is all IPv4 addresses, but should be configured to specific addresses
           for security reasons
       ssh_host_key_files:
-        default: []
+        default: undefined
         type: list
         description: Host keys for sshd. If empty ['/etc/ssh/ssh_host_rsa_key', '/etc/ssh/ssh_host_ecdsa_key',
           '/etc/ssh/ssh_host_ed25519_key'] will be used, as far as supported by the
@@ -318,15 +318,15 @@ argument_specs:
         description: Specifies the maximum number of concurrent unauthenticated connections
           to the SSH daemon.
       ssh_macs:
-        default: []
+        default: undefined
         type: list
         description: Change this list to overwrite macs. Defaults found in `defaults/main.yml`
       ssh_kex:
-        default: []
+        default: undefined
         type: list
         description: Change this list to overwrite kexs. Defaults found in `defaults/main.yml`
       ssh_ciphers:
-        default: []
+        default: undefined
         type: list
         description: Change this list to overwrite ciphers. Defaults found in `defaults/main.yml`
       ssh_custom_options: