Add a test for executing i386 applications on amd64 systems

[martinkunkel2]

This adds a test for issue #350 Depends on fix https://github.com/nestybox/sysbox-runc/pull/95

Before applying the fix

# docker exec aa4f7bb11871 bash -c echo 'int main(){return 0;}' | gcc -m32 -o test-i386 -xc - (status=0):
# 
# docker exec aa4f7bb11871 bash -c ./test-i386 (status=159):

After applying the fix

Executing tests/multilib ... 
1..1
ok 1 i386 application in amd64 system using multilib (sysbox issue 350)