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: I169a5e3b7a9d80e18e389ae4645d2c5bbdae2a6f
Merge "Add troubleshoot to baremetal PXE template."