Coverity: Fix resource leak in xen driver

Coverity: Fix resource leak in xen driver

Coverity logs:

Error: RESOURCE_LEAK:
/builddir/build/BUILD/libvirt-0.9.10/src/xen/xen_inotify.c:103: alloc_fn: Calling allocation function "xenDaemonLookupByUUID".
/builddir/build/BUILD/libvirt-0.9.10/src/xen/xend_internal.c:2534: alloc_fn: Storage is returned from allocation function "virGetDomain".
/builddir/build/BUILD/libvirt-0.9.10/src/datatypes.c:191: alloc_arg: "virAlloc" allocates memory that is stored into "ret".
/builddir/build/BUILD/libvirt-0.9.10/src/util/memory.c:101: alloc_fn: Storage is returned from allocation function "calloc".
/builddir/build/BUILD/libvirt-0.9.10/src/util/memory.c:101: var_assign: Assigning: "*((void **)ptrptr)" = "calloc(1UL, size)".
/builddir/build/BUILD/libvirt-0.9.10/src/datatypes.c:210: return_alloc: Returning allocated memory "ret".
/builddir/build/BUILD/libvirt-0.9.10/src/xen/xend_internal.c:2534: var_assign: Assigning: "ret" = "virGetDomain(conn, name, uuid)".
/builddir/build/BUILD/libvirt-0.9.10/src/xen/xend_internal.c:2541: return_alloc: Returning allocated memory "ret".
/builddir/build/BUILD/libvirt-0.9.10/src/xen/xen_inotify.c:103: var_assign: Assigning: "dom" =  storage returned from "xenDaemonLookupByUUID(conn, rawuuid)".
/builddir/build/BUILD/libvirt-0.9.10/src/xen/xen_inotify.c:126: leaked_storage: Variable "dom" going out of scope leaks the storage it points to.

Error: RESOURCE_LEAK:
/builddir/build/BUILD/libvirt-0.9.10/src/xen/xen_hypervisor.c:2742: alloc_fn: Calling allocation function "fopen".
/builddir/build/BUILD/libvirt-0.9.10/src/xen/xen_hypervisor.c:2742: var_assign: Assigning: "cpuinfo" =  storage returned from "fopen("/proc/cpuinfo", "r")".
/builddir/build/BUILD/libvirt-0.9.10/src/xen/xen_hypervisor.c:2763: noescape: Variable "cpuinfo" is not freed or pointed-to in function "xenHypervisorMakeCapabilitiesInternal".
/builddir/build/BUILD/libvirt-0.9.10/src/xen/xen_hypervisor.c:2574:45: noescape: "xenHypervisorMakeCapabilitiesInternal" does not free or save its pointer parameter "cpuinfo".
/builddir/build/BUILD/libvirt-0.9.10/src/xen/xen_hypervisor.c:2768: leaked_storage: Variable "cpuinfo" going out of scope leaks the storage it points to.

Error: RESOURCE_LEAK:
/builddir/build/BUILD/libvirt-0.9.10/src/xen/xen_hypervisor.c:2752: alloc_fn: Calling allocation function "fopen".
/builddir/build/BUILD/libvirt-0.9.10/src/xen/xen_hypervisor.c:2752: var_assign: Assigning: "capabilities" =  storage returned from "fopen("/sys/hypervisor/properties/capabilities", "r")".
/builddir/build/BUILD/libvirt-0.9.10/src/xen/xen_hypervisor.c:2763: noescape: Variable "capabilities" is not freed or pointed-to in function "xenHypervisorMakeCapabilitiesInternal".
/builddir/build/BUILD/libvirt-0.9.10/src/xen/xen_hypervisor.c:2574:60: noescape: "xenHypervisorMakeCapabilitiesInternal" does not free or save its pointer parameter "capabilities".
/builddir/build/BUILD/libvirt-0.9.10/src/xen/xen_hypervisor.c:2768: leaked_storage: Variable "capabilities" going out of scope leaks the storage it points to.
(cherry picked from commit e91e0ab6042879a170b22bb942cf4051f8900e46)