Allow for overwriting of the SSH keys

[bschonec]

It should be a simple matter to incorporate "< /bin/yes" or "<<<y" into the exec command to allow for overwriting of the SSH key. This would help to enforce SSH key rotation and adhere to CIS recommendations that SSH keys be rotated periodically.

The exec resource would also have to be modified to force a run when (for example) variable $overwrite is true.

[bschonec]

#84