Fix DMI uuid parsing.

valgrind was complaining that virUUIDParse was depending on
an uninitialized value.  Indeed it was; virSetHostUUIDStr()
didn't initialize the dmiuuid buffer to 0's, meaning that
anything after the string read from /sys was uninitialized.
Clear out the dmiuuid buffer before use, and make sure to
always leave a \0 at the end.
Signed-off-by: NChris Lalancette <clalance@redhat.com>

src/util/uuid.c

@@ -286,7 +286,8 @@ virSetHostUUIDStr(const char *uuid)
         return EEXIST;
 
     if (!uuid) {
-        if (!getDMISystemUUID(dmiuuid, sizeof(dmiuuid))) {
+        memset(dmiuuid, 0, sizeof(dmiuuid));
+        if (!getDMISystemUUID(dmiuuid, sizeof(dmiuuid) - 1)) {
             if (!virUUIDParse(dmiuuid, host_uuid))
                 return 0;
         }