tests/docker: make test-full build all targets, not none

Fix common.rc to avoid passing an empty --target-list= option to configure.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Message-id: 1465224417-141321-3-git-send-email-pbonzini@redhat.com
Signed-off-by: NFam Zheng <famz@redhat.com>

tests/docker/common.rc

@@ -24,7 +24,7 @@ requires()
 build_qemu()
 {
     $QEMU_SRC/configure \
-        --target-list="${TARGET_LIST}" \
+        ${TARGET_LIST:+"--target-list=${TARGET_LIST}"} \
         --prefix="$PWD/install" \
         $EXTRA_CONFIGURE_OPTS \
         "$@"