lib/odp-util: Skip ignored fields when parsing and formatting.

When a whole field of a key value is ignored, skip it when formatting
the key, and allow it to be left out when parsing the key from a
string.  However, when the 'verbose' formatting is requested those are
still formatted, as it may help in debugging.

Now the named key fields can also be given in arbitrary order.
Duplicate field values are not checked for, so the last one will
remain in effect.

Signed-off-by: Jarno Rajahalme <[email protected]>
Acked-by: Ben Pfaff <[email protected]>