client: Add ping-timeout to statedump

The ping timeout value of a client xlator can be seen by,

># cat $META/graphs/active/vol-client-0/private |grep ping_timeout
ping_timeout = 42

where $META is /<fuse-mountpt>/.meta

Change-Id: I4f68f184fc3f30871269a23fc4a82a1378396058
Signed-off-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-on: http://review.gluster.org/8321
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>