nix/keys: Use 0600 as the default permissions.

Only using this for legacy options could introduce unexpected behaviour
when switching to the new configuration if the user just appends a .text
to its configuration values and could possibly lead to services that
refuse to work, especially when it comes to OpenSSH.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Fix VM tests for hetzner and none backends.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
(cherry picked from commit 66aeeb201446a94f7ebb59461b5efcbc02019a9d)
tests: Add Archive::Cpio to all the coordinators.

This is needed in order to build the initrd for the target machines and
we don't have access to external network resources within the VM test.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
(cherry picked from commit 1bd7182bc1609d602e6193ee4665a6dce45aded4)
tests: Disable packet filtering on all VM tests.

This is only a source for more errors, confusion, more complexity and we
really don't want to test the packet filter here, because we already
have tests in NixOS directly.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
(cherry picked from commit 8feb9223bc5d43517bf4acd93b89a84802d90d05)