Storage connection reference: move persistent dir to /var/lib/vdsm

The current persistent dir for connection reference is
/var/run/vdsm/connections, however /var/run is tmpfs so it's not truely
persistent enough. According to the WIKI page [1], the connection
reference is meant to survive reboots. This patch moves the persistent
dir to /var/lib/vdsm/connections to achieve this.

[1] http://www.ovirt.org/Features/ConnectionReferences#Description

Change-Id: Iff758232ded5ef730d24f36d5d493255fc7775d0
Signed-off-by: Zhou Zheng Sheng <zhshzhou@linux.vnet.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/13087
Reviewed-by: Mark Wu <wudxw@linux.vnet.ibm.com>
Reviewed-by: Ayal Baron <abaron@redhat.com>