Make use of Magic SysRq via the BMC serial connection

[srcshelton]

Is your feature request related to a problem? Please describe.

As a TP2 user,
I would like to make maximal use of the existing options for interaction between the BMC and installed nodes
so that the TP2 can behave a little more like server-class systems with tight BMC integration.

Describe the solution you'd like

The UI 'Power' options could be updated to differentiate between a soft reset/power-down and a hard reset/power-down:

• Fuzzy but presumably possible: if the user chooses to enter per-node user/root credentials, then on soft-reset the BMC could open a serial connection a look for an active shell session or login prompt, and then automagically issue a 'shutdown -r now' or 'shutdown -h now' command - it could even steal output and display the result in the BMC Web UI (if there was no active session?);

• Via an alternate UI option or if the node appears unresponsive, then the BMC could send Sync/Umount/Reboot (or Crash) Magic SysRq sequences via the serial connection (which the kernel should respond to regardless of whether there's a session in progress or even a full-screen application running) before cutting power.