Add troubleshoot to baremetal PXE template.

We recently added an optional troubleshoot parameter to
diskimage_builder which defaults to 0 (false).

This commit adds the option to the Nova pxe_config.template
so it will be easier for people to find should they need to
enable troubleshooting mode.

Change-Id: I24cea1bb621b267a79fb170ace749fae14d06c30
Merge "Add troubleshoot to baremetal PXE template."