Simplify crypto.yml checks with blocks

[rndmh3ro]

Is your feature request related to a problem? Please describe.
Right now there's much duplicated code in the crypto.yaml task-file.

Describe the solution you'd like

We should use blocks

- name: block
  block:
    - name: set hostkeys according to openssh-version
      set_fact:
        ssh_host_key_files: ['/etc/ssh/ssh_host_rsa_key', '/etc/ssh/ssh_host_ecdsa_key', '/etc/ssh/ssh_host_ed25519_key']

    - name: set macs according to openssh-version if openssh >= 7.6
      set_fact:
        ssh_macs: '{{ ssh_macs_76_default }}'

    - name: set ciphers according to openssh-version if openssh >= 6.6
      set_fact:
        ssh_ciphers: '{{ ssh_ciphers_66_default }}'

  when: sshd_version.stdout is version('6.3', '>=') and not ssh_host_key_files

[rndmh3ro]

Fixed by #305, thanks @schurzi!