iec-sonar: Disable git submodule cloning

SonarQube should be limited to scanning the IEC repository contents
and not its (massive) collection of git submodules which include various
upstream components (including the full K8s source code, among other
large code bases).

Although we apply some inclusion/exclusion filtering as part of
SonarQube configuration, it seems that the large collection of git
submodules interferes with log collection and upload; hence disable
cloning git submodules before running SonarQube.
This is an attempt at fixing the ever-hanging iec-sonar job in CI.

Change-Id: If6b9b205d8f1924ca8180787a92415494461d5b7
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>