Bug 1335477: Group by query returns different results in 2 builds

Reset the noExePreds flag in the MDAM key when we add
partitioning key predicates during preCodeGen. Those added
predicate can contain executor predicates that must not be
suppressed.

Also fixed an issue found in bug 1306836, where the syntax for
selecting specific partitions (salt buckets) was ignored for
coprocessor aggregation (simple count(*)). This syntax now disables
the coprocessor aggregate.

Change-Id: Id8dc0b7769f31a700bb459c424caada2f447a6ae