tests: fix /var race in multipath.partition part 2

This fixes the same race condition in a previous PR coreos#2457 [0]. The
difference is that in PR coreos#2758 [1], `mpath-var-lib-containers.service`
uses mkdir to create `/var/lib/containers` and in some cases it will race
against `ostree-remount.service` during the short window `/var` is
read-only. Have `mpath-var-lib-containers.service` run after
`ostree-remount.service` to resolve this.

[0] coreos#2457
[1] coreos#2758

mantle/kola/tests/misc/multipath.go

@@ -62,6 +62,9 @@ systemd:
         ConditionFirstBoot=true
         Requires=dev-mapper-mpatha.device
         After=dev-mapper-mpatha.device
+        # See https://github.com/coreos/coreos-assembler/pull/2457
+        # and https://github.com/openshift/os/issues/743
+        After=ostree-remount.service
         Before=kubelet.service
         DefaultDependencies=no
 
@@ -78,8 +81,6 @@ systemd:
       contents: |
         [Unit]
         Description=Mount /var/lib/containers
-        # See https://github.com/coreos/coreos-assembler/pull/2457
-        After=ostree-remount.service
         After=mpath-var-lib-containers.service
         Before=kubelet.service