test: Add distribution tests for several architectures and kernel versions

The new tests check build and a simple case with pasta sending a
short message in both directions (namespace to init, init to
namespace).

Tests cover a mix of Debian, Fedora, OpenSUSE and Ubuntu combinations
on aarch64, i386, ppc64, ppc64le, s390x, x86_64.

Builds tested starting from approximately glibc 2.19, gcc 4.7, and
actual functionality approximately from 4.4 kernels, glibc 2.25,
gcc 4.8, all the way up to current glibc/gcc/kernel versions.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

test/run

@@ -64,6 +64,7 @@ run() {
 
 	setup build
 	test build
+	test distro
 
 	setup pasta
 	test ndp