SPEC-2903: Use a wrapper instead of constructing a command

SPEC-2903: Use a wrapper instead of constructing a command

This patch change the way we ran afm-util commands by using a simple
wrapper.
Furthermore, since we are in a loop, let's reset all variable
(SERVICE_PLATFORM/etc..) to 0 at the beginning of the loop.

Extra-furthermore: restore the unzip error code test, but in non-fatal
way, since busybox unzip seems to dont like our CRC.

Bug-AGL: SPEC-2903

Change-Id: I5d7357fd74307ed69a6675beac57d8601fdcdb52
Signed-off-by: Corentin LABBE <clabbe@baylibre.com>