If any nova-manage command fails in an unexpected way and
it bubbles back up to main() the return code will be 1.
There are some commands like archive_deleted_rows,
map_instances and heal_allocations which return 1 for flow
control with automation systems. As a result, those tools
could be calling the command repeatedly getting rc=1 thinking
there is more work to do when really something is failing.
This change makes the unexpected error code 255, updates the
relevant nova-manage command docs that already mention return
codes in some kind of list/table format, and adds an upgrade
release note just to cover our bases in case someone was for
some weird reason relying on 1 specifically for failures rather
than anything greater than 0.
Change-Id: I2937c9ef00f1d1699427f9904cb86fe2f03d9205
Closes-Bug: #1840978
df2845308d