allow custom rc-imaging scripts and show all disks for 10.13

[erikng]

What does this PR do?

This PR makes it where Disk Utility will show the disks vs the Volumes, allowing an Imagr user to easily format a disk from APFS to HFS and vice versa. The default UI of Disk Utility hides this feature.

This PR also allows an admin to setup a custom rc.imaging script to do any number of things.

Simply add STARTTERMINAL=Custom to your config.mk file and make a custom file, places in the rc-imaging folder.

Previous Behavior

Previously the makefile used printf to generate the rc.imaging file and did not setup Disk Utility properly for 10.13

New Behavior

The makefile now calls out to the rc-imaging folder for these scripts, allowing an admin to easily write a script to do any number of custom things.

The admin should add a file called custom in the rc-imaging folder. A gitignore has also been setup for this file.

Example script:

#!/bin/bash
OS=`/usr/bin/sw_vers -productVersion`
if [[ "$OS" == *10.13* ]]
  then
    defaults write /var/root/Library/Preferences/com.apple.DiskUtility.plist SidebarShowAllDevices -bool TRUE
fi
/bin/mkdir -p /Volumes/imagrtest
/sbin/mount -t smbfs //username:password@IPADDRESS/sharepath /Volumes/imagrtest
/Applications/Utilities/Terminal.app/Contents/MacOS/Terminal

[grahamgilbert]

This basically always copies over rc-imaging/custom. Unless I'm mistaken I don't see a scenario where Imagr actually opens.

[grahamgilbert]

Scratch that, I was mistaken.