automatically "fix" packer json file.

[mySYSMON]

Adding packer fix to automatically handle common json packer error.

[mySYSMON]

Fixes this error
Using Packer to build the windows_2016 Box. This can take 90-180 minutes depending on bandwidth and hardware.
Error: Failed to prepare build: "virtualbox-iso"

1 error occurred:
* Deprecated configuration key: 'iso_checksum_type'. Please call packer fix
against your template to update your template to be compatible with the current
version of Packer. Visit https://www.packer.io/docs/commands/fix/ for more
detail.

==> Builds finished but no artifacts were created.
Something went wrong while attempting to build the windows_2016 box.
To file an issue, please visit https://github.com/clong/DetectionLab/issues/