I'm afraid Impala is not yet able to recognize that only two partitions need to be scanned. We're aware of the gap and that specific optimization is tracked by:
https://issues.apache.org/jira/browse/IMPALA-2108
For now, you can manually rewrite your query as suggested in the JIRA as follows:
select id, yyyymmdd, group_id, test from dwh.table where
((id='1a' and yyyymmdd=20170815 and group_id=1) OR (id='2b' and yyyymmdd=20170811 and group_id=2))
AND
((yyyymmdd=20170811 and group_id=2) OR (yyyymmdd=20170815 and group_id=1))
or alternatively, use a union:
select id, yyyymmdd, group_id, test from dwh.table where
id='1a' and yyyymmdd=20170815 and group_id=1
union all
select id, yyyymmdd, group_id, test from dwh.table where
id='2b' and yyyymmdd=20170811 and group_id=2