upload: raising an execption on bad gzip files

Raising an exception to mimic past bahavior

Change-Id: I76ae1a09b52a53a09e351c97eccad300952ae539
Bug-Url: https://bugzilla.redhat.com/1156107
Signed-off-by: Simone Tiraboschi <stirabos@redhat.com>
(cherry picked from commit b79bcd11a2d515dfddb4fc21ac0efc06a334b23e)