Microversion 1.35_ adds support for the ``root_required`` query
parameter to the ``GET /allocation_candidates`` API. It accepts a
comma-delimited list of trait names, each optionally prefixed with ``!``
to indicate a forbidden trait, in the same format as the ``required``
query parameter. This restricts allocation requests in the response to
only those whose (non-sharing) tree's root resource provider satisfies
the specified trait requirements.
This is to support use cases like, "Land my VM on a host that is capable
of multi-attach," or, "Reserve my Windows-licensed hosts for special
use."
Story: #2005575
Task: #33753
Change-Id: I76cad83248920fa71da122711f1f763c4ebdb1ba
b733786a0a