engineencryptutils: cleanup

Remove dead code.
Remove redundant variables.
Rework to reach somewhat similar structure between functions.
Remove the use of StringHelper.

Not that the result is good... but at least something in the right way.

Change-Id: I9c1004e42ee92347cbf97011e3216a1ac5c23173
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>