Set virt_use_execmem boolean if SELinux is enabled.

If SELinux is enabled, this boolean is required to be able to launch VMs using qemu.
Set the boolean if we're switching the libvirt_type to 'qemu' and SELinux is enabled.

Change-Id: Ieead35aae94c9fa86df1f4829584f71c97dcbeb8

stack.sh

@@ -1345,6 +1345,10 @@ if is_service_enabled n-cpu; then
         if [ ! -e /dev/kvm ]; then
             echo "WARNING: Switching to QEMU"
             LIBVIRT_TYPE=qemu
+            if which selinuxenabled 2>&1 > /dev/null && selinuxenabled; then
+                # https://bugzilla.redhat.com/show_bug.cgi?id=753589
+                sudo setsebool virt_use_execmem on
+            fi
         fi
     fi