Configure lower NFS grace period.

From RFC 3530:
  During the grace period, the server must reject READ and WRITE operations
  and non-reclaim locking requests (i.e., other LOCK and OPEN operations)
  with an error of NFS4ERR_GRACE.

That basically means that all open() calls from clients are blocked until the
grace period is over (90 seconds by default).

We want the grace period as low as possible to speed up the tests. '10'
seconds were tested on Fedora 21 and Ubuntu 15.04 as the hosts.

The test image is rebased to Fedora in order to get 'rpc.nfsd -G <n>' option,
Ubuntu does not support it.

test/images/volumes-tester/nfs/Dockerfile

@@ -12,10 +12,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-FROM ubuntu:14.04
+FROM centos
 MAINTAINER Jan Safranek, jsafrane@redhat.com
-ENV DEBIAN_FRONTEND noninteractive
-RUN apt-get update -qq && apt-get install -y nfs-kernel-server -qq
+RUN yum -y install /usr/bin/ps nfs-utils && yum clean all
 RUN mkdir -p /exports
 ADD run_nfs.sh /usr/local/bin/
 ADD index.html /exports/index.html

test/images/volumes-tester/nfs/Makefile

@@ -1,6 +1,6 @@
 all: push
 
-TAG = 0.2
+TAG = 0.3
 
 container:
 	docker build -t gcr.io/google_containers/volume-nfs . # Build new image and automatically tag it as latest

test/images/volumes-tester/nfs/run_nfs.sh

@@ -31,7 +31,8 @@ function start()
     /usr/sbin/rpc.mountd -N 2 -N 3 -V 4 -V 4.1
 
     /usr/sbin/exportfs -r
-    /usr/sbin/rpc.nfsd -N 2 -N 3 -V 4 -V 4.1 2
+    # -G 10 to reduce grace time to 10 seconds (the lowest allowed)
+    /usr/sbin/rpc.nfsd -G 10 -N 2 -N 3 -V 4 -V 4.1 2
 
     echo "NFS started"
 }