Provide root privilege access to QEMU 9p proxy filesystem using socket
communication.

Proxy helper is started by root user as:
~ # virtfs-proxy-helper -f|--fd <socket descriptor> -p|--path <path-to-share>
Signed-off-by: NM. Mohan Kumar <mohan@in.ibm.com>
Signed-off-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>