volume subdir has no integ-test Makefile rule

[ginglis13]

Right now the top level Makefile uses a list of sub-directories to target running integration tests:

firecracker-containerd/Makefile

Lines 14 to 16 in 279a03c

	SUBDIRS:=agent runtime examples firecracker-control/cmd/containerd snapshotter docker-credential-mmds volume
	TEST_SUBDIRS:=$(addprefix test-,$(SUBDIRS))
	INTEG_TEST_SUBDIRS:=$(addprefix integ-test-,$(SUBDIRS))

For example, the volume directory is included in this list, but its Makefile does not contain an integ-test rule, resulting in failure. The integration test(s) for volume live under the snapshotter directory.

Is there a reason why volume integ tests are under snapshotter ? If there is, we can just add a no-op integ-test rule to the volume Makefile. If not, maybe we can refactor to just pull that test into the volume directory.

e: answering the above question: volume is provided as a package and consumed in the volume integ test. moving this test to the volume dir would introduce an import cycle.