change dep for docker-selinux in centos-7+

Use the policy files provided by CentOS for docker by depending on
docker-selinux.

Signed-off-by: Andrew Hsu <andrewhsu@docker.com>

hack/make/.build-rpm/docker-engine.spec

@@ -86,7 +86,11 @@ Requires: device-mapper >= 1.02.90-2
 # RE: rhbz#1195804 - ensure min NVR for selinux-policy
 %if 0%{?with_selinux}
 Requires: selinux-policy >= %{selinux_policyver}
+%if 0%{?centos} >= 7
+Requires(pre): docker-selinux
+%else
 Requires(pre): %{name}-selinux >= %{version}-%{release}
+%endif # centos 7+
 %endif # with_selinux
 
 # conflicting packages