bitbake: cooker/command: Add error state for the server and use for pre_serve errors

bitbake: cooker/command: Add error state for the server and use for pre_serve errors

Currently if errors occur when starting the PR service, there is a race that
occurs since the UI runs various commands including starting builds before
processing the CookerExit(). By adding the error state and refusing to run
async commands in this mode, builds are prevented from starting and the
UI reaches the exit code with the system shutting down cleanly.

(Bitbake rev: 42fa34142ea685f91115a551e74416ca28ef1c91)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>