libvirt-machine-props: Refactor system props code a little

Put all the code to add troubleshoot log button and dialog into a
separate method.
libvirt-machine-props: Change placement of troubleshoot log

Put the troubleshoot log button between resource stats and resource
controls, as per new UI mockups.
libvirt-machine-props: Add 'Force Shutdown' button

Add'Force Shutdown' button to properties under 'System' page, next to
'Troubleshooting log' button.

This is part of move of sidebar contents to main view before sidebar can
be dropped.