Add query field flags

Some fields (e.g. “name”) should be treated specially when comparing for
equality. Hypervisor names should use normal rules, but for node names,
“node2” should be equivalent with “node2.example.com”.

To make these differences, a new field for flags is added to the query
fields. It is not added to ”objects.QueryFieldDefinition” (the first
item) as it would be exported to clients, something not desired for
these internal rules. Instead, an additional field is added.

Other special rules, e.g. “a list of strings” for an instance's
secondary nodes, can be implemented as flags, too.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>