Fix otapreopt parameters reading

The code was missing a break in the switch statement and was always
failing the default CHECK.

Also, move the logging to standard error to make it obvious the test
failed (instead of relying on the exit code which can be easily missed).

Test: installd_otapreopt_test
Bug: 71993124
Change-Id: Iaf29ebc9b930981bf3b75c33e63e940139421e1d