Additional private key resolution method
Additional private key resolution method

- Added an additional private key resolution method to keep it
  compatible with previous versions of vcair driver and allow
  other drivers to use `:ssh_options` as found in some places
  of the chef provisioning documentation

Signed-off-by: Khaled Janania <4ad60e10be6f19b7e7b8a19ecd1bab87c44c8056@ncr.com>

chef/chef-provisioning-fog,chef/chef-provisioning-fog