AllLinesParser: Enable draining of stdout

If draining isn't enabled, the AllLinesParser and Script timeout,
because noone is reading the full output of the process and so
the process can't finish and will timeout.

This was noticed while `drbdsetup events --now` was writing around 1200 lines
into stdout and always hang in a timeout.

Author: rp-

utils/src/main/java/com/cloud/utils/script/OutputInterpreter.java

@@ -137,6 +137,11 @@ public String interpret(BufferedReader reader) throws IOException {
         public String getLines() {
             return allLines;
         }
+
+        @Override
+        public boolean drain() {
+            return true;
+        }
     }
 
     public static class LineByLineOutputLogger extends OutputInterpreter {

utils/src/test/java/com/cloud/utils/ScriptTest.java

@@ -111,6 +111,20 @@ public String interpret(BufferedReader reader) throws IOException {
         Assert.assertNotNull(value);
     }
 
+    @Test
+    public void executeWithOutputInterpreterAllLineReader() {
+        Assume.assumeTrue(SystemUtils.IS_OS_LINUX);
+        OutputInterpreter.AllLinesParser parser = new OutputInterpreter.AllLinesParser();
+        Script script = new Script("seq");
+        script.add("-f");
+        script.add("my text to test cloudstack %g");
+        script.add("4096"); // AllLinesParser doesn't work with that amount of data
+        String value = script.execute(parser);
+        // it is a stack trace in this case as string
+        Assert.assertNull(value);
+        Assert.assertEquals(129965, parser.getLines().length());
+    }
+
     @Test
     public void runSimpleBashScriptNotExisting() {
         Assume.assumeTrue(SystemUtils.IS_OS_LINUX);