Automatic merge from submit-queue

read gluster log to surface glusterfs plugin errors properly in describe events

glusterfs.go does not properly expose errors as all mount errors go to a log file, I propose we read the log file to expose the errors without asking the users to 'go look at this log'

This PR does the following:
1.  adds a gluster option for log-level=ERROR to remove all noise from log file
2.  change log file name and path based on PV + Pod name - so specific per PV and Pod
3.  create a utility to read the last two lines of the log file when failure occurs

old behavior:
```
  13s	13s	1	{kubelet 127.0.0.1}		Warning	FailedMount	Unable to mount volumes for pod "bb-gluster-pod2_default(34b18c6b-070d-11e6-8e95-52540092b5fb)": glusterfs: mount failed: Mount failed: exit status 1
Mounting arguments: 192.168.234.147:myVol2 /var/lib/kubelet/pods/34b18c6b-070d-11e6-8e95-52540092b5fb/volumes/kubernetes.io~glusterfs/pv-gluster glusterfs [log-file=/var/lib/kubelet/plugins/kubernetes.io/glusterfs/pv-gluster/glusterfs.log]
Output: Mount failed. Please check the log file for more details.
```

improved behavior: (updated after suggestions from community)
```
  34m		34m		1	{kubelet 127.0.0.1}			Warning		FailedMount	Unable to mount volumes for pod "bb-multi-pod1_default(e7d7f790-0d4b-11e6-a275-52540092b5fb)": glusterfs: mount failed: Mount failed: exit status 1
Mounting arguments: 192.168.123.222:myVol2 /var/lib/kubelet/pods/e7d7f790-0d4b-11e6-a275-52540092b5fb/volumes/kubernetes.io~glusterfs/pv-gluster2 glusterfs [log-level=ERROR log-file=/var/lib/kubelet/plugins/kubernetes.io/glusterfs/pv-gluster2/bb-multi-pod1-glusterfs.log]
Output: Mount failed. Please check the log file for more details.

 the following error information was pulled from the log to help resolve this issue: 
[2016-04-28 14:21:29.109697] E [socket.c:2332:socket_connect_finish] 0-glusterfs: connection to 192.168.123.222:24007 failed (Connection timed out)
[2016-04-28 14:21:29.109767] E [glusterfsd-mgmt.c:1819:mgmt_rpc_notify] 0-glusterfsd-mgmt: failed to connect with remote-host: 192.168.123.222 (Transport endpoint is not connected)

```

also this PR is alternate approach to :  #24624