issue #29780: reintroduce fix for GVT failure by setting default loca…

…le to utf8

the original fix was reverted due to failure in zos, fixed by adding guard code for zos

dev/fattest.simplicity/src/componenttest/topology/impl/LibertyFileManager.java

@@ -15,6 +15,8 @@
 import java.io.BufferedInputStream;
 import java.io.FileNotFoundException;
 import java.io.InputStream;
+import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
@@ -267,7 +269,14 @@ static LogSearchResult findStringsInFileCommon(List<String> regexpList,
                 totalSkipped += skipped;
             }
 
-            UnbufferedInputStreamReader rawReader = new UnbufferedInputStreamReader(input, fileToSearch.getEncoding());
+            // UTF-8 by default so that GVT tests doesn't fail in non English locale
+            OperatingSystem os = fileToSearch.getMachine().getOperatingSystem();
+            Charset fileEncoding = StandardCharsets.UTF_8;
+            if (os == OperatingSystem.ZOS) {
+                fileEncoding = fileToSearch.getEncoding();
+            }
+
+            UnbufferedInputStreamReader rawReader = new UnbufferedInputStreamReader(input, fileEncoding);
             reader = new LineReader(rawReader);
 
             Log.finer(CLASS, method, "Now looking for strings " + regexpList