Make lava_dispatcher not depend on lava_dispatcher_host
Move any functionality that lava_dispatcher depends on from
lava_dispatcher_host
to lava_common.device_mappings
.
This was mainly related to writing device mappings in YAML to a
job working directories.
Currently it is very difficult to install lava_dispatcher on Debian 11 because lava_dispatcher host depends on python3-bpfcc (>= 0.21)
which is not packaged for Debian 11. (without backports)