Have to capture for backreference

Author: jasontedor

qa/evil-tests/src/test/java/org/elasticsearch/monitor/os/EvilOsProbeTests.java

@@ -39,10 +39,10 @@ public void testOsPrettyName() throws IOException  {
             final List<String> lines = Files.readAllLines(PathUtils.get("/etc/os-release"));
             for (final String line : lines) {
                 if (line != null && line.startsWith("PRETTY_NAME=")) {
-                    final Matcher matcher = Pattern.compile("PRETTY_NAME=(?:\"?|'?)?([^\"']+)\\1").matcher(line.trim());
+                    final Matcher matcher = Pattern.compile("PRETTY_NAME=(\"?|'?)?([^\"']+)\\1").matcher(line.trim());
                     assert matcher.matches() : line;
-                    assert matcher.groupCount() == 1 : line;
-                    final String prettyName = matcher.group(1);
+                    assert matcher.groupCount() == 2 : line;
+                    final String prettyName = matcher.group(2);
                     assertThat(osInfo.getPrettyName(), equalTo(prettyName));
                     return;
                 }

server/src/main/java/org/elasticsearch/monitor/os/OsProbe.java

@@ -551,10 +551,10 @@ private String getPrettyName() throws IOException {
             if (maybePrettyNameLine.isPresent()) {
                 // we trim since some OS contain trailing space, for example, Oracle Linux Server 6.9 has a trailing space after the quote
                 final String trimmedPrettyNameLine = maybePrettyNameLine.get().trim();
-                final Matcher matcher = Pattern.compile("PRETTY_NAME=(?:\"?|'?)?([^\"']+)\\1").matcher(trimmedPrettyNameLine);
+                final Matcher matcher = Pattern.compile("PRETTY_NAME=(\"?|'?)?([^\"']+)\\1").matcher(trimmedPrettyNameLine);
                 assert matcher.matches() : trimmedPrettyNameLine;
-                assert matcher.groupCount() == 1 : trimmedPrettyNameLine;
-                return matcher.group(1);
+                assert matcher.groupCount() == 2 : trimmedPrettyNameLine;
+                return matcher.group(2);
             } else {
                 return Constants.OS_NAME;
             }