fix enablekdump for redhat7.6 and 7.6-alt nfs vers 4 support

[bybai]

The PR is to fix issue

#5712

The modification include

nfs vers in redhat7.6 and 7.6-alt is 4, enablekdump hard code mount -o vers=3 ..., this cause error like:

[root@f5u14 ~]# /bin/mount -o vers=3 10.6.13.10:/kdumpdir /root/bai
mount.nfs: requested NFS version or transport protocol is not supported

The UT result

After this fix, UT:

[root@c910f03c09k09 postscripts]# updatenode c910f03c09k11 enablekdump
c910f03c09k11: vpdupdate is not supported on the pSeries KVM Guest platform
c910f03c09k11: updating VPD database
c910f03c09k11: trying to download postscripts...
c910f03c09k11: postscripts downloaded successfully
c910f03c09k11: trying to get mypostscript from 10.3.9.9...
c910f03c09k11: Running postscript: enablekdump
c910f03c09k11: ++ /usr/sbin/rpcinfo -p 10.3.9.9
c910f03c09k11: ++ grep -w nfs
c910f03c09k11: ++ awk '/tcp/{print $2}'
c910f03c09k11: ++ sort
c910f03c09k11: + nfsvers='3
c910f03c09k11: 4'
c910f03c09k11: + nfsver=0
c910f03c09k11: + '[' -n '3
c910f03c09k11: 4' ']'
c910f03c09k11: + for i in '$nfsvers'
c910f03c09k11: + '[' 3 -eq 3 ']'
c910f03c09k11: + '[' grep -w nfs /proc/filesystems ']'
c910f03c09k11: + nfsver=3
c910f03c09k11: + break
c910f03c09k11: + '[' 3 -ne 0 ']'
c910f03c09k11: + /bin/mount -o vers=3 10.3.9.9:/kdumpdir /mnt
c910f03c09k11: + set +x
c910f03c09k11: postscript: enablekdump exited with code 0
c910f03c09k11: Running of postscripts has completed.

[robin2008]

Need to print a message when no NFS server ready.

[robin2008]

Only mount when nfs server is okay.