Make bash troubleshooting configurable

Adds a new 'troubleshooting' function which encapsulates
the things we might want to do when something bad happens.
Typically this is echo'ing a simple message and launching a
bash shell.

The new troubleshooting function also makes use of a new
'troubleshoot' kernel param which if specific will allow you to
hang the deployment process and interactively debug the deploy_ramdisk
via a bash shell on a console.

Troubleshoot is disabled by default.

Fixes LP Bug #1191043.

Change-Id: I2cba8a9674075ba7e420027d40ef8cbe756cf07e
Merge "Make bash troubleshooting configurable"