virjson: add convenience wrapper for appending string to array

Upcoming patches need an array of strings for use in QMP
block-dirty-bitmap-merge.  A convenience wrapper cuts down
on the verbosity of creating the array, similar to the
existing virJSONValueObjectAppendString().
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/libvirt_private.syms

@@ -2092,6 +2092,7 @@ virISCSIScanTargets;
 # util/virjson.h
 virJSONStringReformat;
 virJSONValueArrayAppend;
+virJSONValueArrayAppendString;
 virJSONValueArrayForeachSteal;
 virJSONValueArrayGet;
 virJSONValueArraySize;

src/util/virjson.c

@@ -795,6 +795,21 @@ virJSONValueArrayAppend(virJSONValuePtr array,
 }
 
 
+int
+virJSONValueArrayAppendString(virJSONValuePtr object,
+                              const char *value)
+{
+    virJSONValuePtr jvalue = virJSONValueNewString(value);
+    if (!jvalue)
+        return -1;
+    if (virJSONValueArrayAppend(object, jvalue) < 0) {
+        virJSONValueFree(jvalue);
+        return -1;
+    }
+    return 0;
+}
+
+
 int
 virJSONValueObjectHasKey(virJSONValuePtr object,
                          const char *key)

src/util/virjson.h

@@ -138,6 +138,8 @@ int virJSONValueObjectRemoveKey(virJSONValuePtr object, const char *key,
                                 virJSONValuePtr *value)
     ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2);
 
+int virJSONValueArrayAppendString(virJSONValuePtr object, const char *value);
+
 virJSONValuePtr virJSONValueFromString(const char *jsonstring);
 char *virJSONValueToString(virJSONValuePtr object,
                            bool pretty);