docker: avoid dependency on 'realpath' package

The 'realpath' executable is shipped in a separate package that isn't
installed by default on some distros.

We already use 'readlink -e' (provided by GNU coreutils) in some other
part of the code, so let's settle for that instead.
Signed-off-by: NSascha Silbe <silbe@linux.vnet.ibm.com>
Message-Id: <1473192351-601-3-git-send-email-silbe@linux.vnet.ibm.com>
Signed-off-by: NFam Zheng <famz@redhat.com>

tests/docker/Makefile.include

@@ -116,7 +116,7 @@ docker-run-%: docker-qemu-src
 				-e EXTRA_CONFIGURE_OPTS=$(EXTRA_CONFIGURE_OPTS) \
 				-e V=$V -e J=$J -e DEBUG=$(DEBUG)\
 				-e CCACHE_DIR=/var/tmp/ccache \
-				-v $$(realpath $(DOCKER_SRC_COPY)):/var/tmp/qemu:z$(COMMA)ro \
+				-v $$(readlink -e $(DOCKER_SRC_COPY)):/var/tmp/qemu:z$(COMMA)ro \
 				-v $(DOCKER_CCACHE_DIR):/var/tmp/ccache:z \
 				qemu:$(IMAGE) \
 				/var/tmp/qemu/run \