Always trait the compute node RP with COMPUTE_NODE

We have at least one use case [1] for identifying resource providers
which represent compute nodes. There are a few ways we could do that
hackishly (e.g. [2], [3]) but the clean way is to have nova-compute mark
the provider with a trait, since nova-compute knows which one it is
anyway.

This commit uses the COMPUTE_NODE trait for this purpose, and bumps the
os-traits requirement to 1.1.0 where it is introduced.

Arguably this is a no-op until something starts using it, but a release
note is added anyway warning that all compute nodes should be upgraded
to ussuri (or the trait added manually) for the trait to be useful.

[1] https://review.opendev.org/#/c/670112/7/nova/cmd/manage.py@2921
[2] Assume a provider with a certain resource class, like MEMORY_MB, is
always a compute node. This is not necessarily future-proof (maybe all
MEMORY_MB will someday reside on NUMA node providers; similar for other
resource classes) and isn't necessarily true in all cases today anyway
(ironic nodes don't have MEMORY_MB inventory) and there's also currently
no easy way to query for that (GET /resource_providers?MEMORY_MB:1 won't
return "full" providers, and you can't ask for :0).
[3] Assume a root provider without the MISC_SHARES_VIA_AGGREGATE trait
is a compute node. This assumes you're only using placement for nova-ish
things.

Change-Id: I4cb9cbe1e02c3f6c6148f73a38d10e8db7e61b1a

requirements.txt

@@ -56,7 +56,7 @@ psutil>=3.2.2 # BSD
 oslo.versionedobjects>=1.35.0 # Apache-2.0
 os-brick>=2.6.2 # Apache-2.0
 os-resource-classes>=0.4.0 # Apache-2.0
-os-traits>=0.16.0 # Apache-2.0
+os-traits>=1.1.0 # Apache-2.0
 os-vif>=1.14.0 # Apache-2.0
 os-win>=3.0.0 # Apache-2.0
 castellan>=0.16.0 # Apache-2.0