remove duplicated 'pillar.get' calls to retrieve the sshd_config and ssh_config pillars.

Change the require_ins used by the key management states in the
config.sls to be conditional based on whether the sshd_config
is managed by the formula

Fixes #130

- generate before running check_mk on the sshd_config
- set permissions on private key
- cope with empty keys

Made a small change to reflect the default sshd_config

By not specifying it, root user's group should be used.

sshd_config