Add troubleshooting override to deploy ramdisk.

We now allow operators to drop into a troubleshooting shell while
booting a deploy ramdisk, without having to have pre-configured their
desire to do so ahead of time, by means of a 10 second pause for them to
press a key.

Change-Id: I05ffa1ebaa95c83dee7bd2a2f52ba4c08928bb10
Merge "Add troubleshooting override to deploy ramdisk."