podvm: fix podvm packaer image build

- install qemu plugin after packer 1.10.0-1

fixes #1616

Signed-off-by: Da Li Liu <liudali@cn.ibm.com>

podvm/Makefile

@@ -77,6 +77,7 @@ $(IMAGE_FILE): $(BINARIES) $(FILES) setopts
 	if [ "${SE_BOOT}" = "1" ] && [ "${ARCH}" = "s390x" ]; then \
 		qemu-img create -f qcow2 "se-${IMAGE_FILE}" 100G; \
 	fi
+	packer plugins install github.com/hashicorp/qemu
 	packer build ${PACKER_DEFAULT_OPTS} ${OPTS} qcow2/$(PODVM_DISTRO)
 	rm -fr toupload
 	rm -f cloud-init.img