Coverity: Fix resource leak in nodeinfo.c

Coverity: Fix resource leak in nodeinfo.c

Error: RESOURCE_LEAK:
/builddir/build/BUILD/libvirt-0.9.10/src/nodeinfo.c:629: alloc_fn: Calling allocation function "fopen".
/builddir/build/BUILD/libvirt-0.9.10/src/nodeinfo.c:629: var_assign: Assigning: "cpuinfo" =  storage returned from "fopen("/proc/cpuinfo", "r")".
/builddir/build/BUILD/libvirt-0.9.10/src/nodeinfo.c:638: leaked_storage: Variable "cpuinfo" going out of scope leaks the storage it points to.
(cherry picked from commit 739cfc31619e9ba8ee450e8762261285093f1f47)