util: fix compile errors caused by moving string functions

commit 7c9a2d8 missed adding in a few #include "virstring.h"s, causing
builds to fail.

src/locking/lock_driver_sanlock.c

@@ -43,6 +43,7 @@
 #include "virfile.h"
 #include "md5.h"
 #include "virconf.h"
+#include "virstring.h"
 
 #include "configmake.h"
 

src/storage/storage_backend_rbd.c

@@ -30,6 +30,7 @@
 #include "virlog.h"
 #include "base64.h"
 #include "viruuid.h"
+#include "virstring.h"
 #include "rados/librados.h"
 #include "rbd/librbd.h"
 

src/storage/storage_backend_sheepdog.c

@@ -32,6 +32,7 @@
 #include "vircommand.h"
 #include "viralloc.h"
 #include "virlog.h"
+#include "virstring.h"
 
 #define VIR_FROM_THIS VIR_FROM_STORAGE
 

tests/storagebackendsheepdogtest.c

@@ -32,6 +32,7 @@
 #include "internal.h"
 #include "testutils.h"
 #include "storage/storage_backend_sheepdog.h"
+#include "virstring.h"
 
 
 typedef struct {