SQL: Fix multi-line CLI commands to join correctly (elastic/x-pack-elasticsearch#3516)

Previously multi-line CLI SQL statements were joined, but the space command was
missing, so a command like:

```
sql> SHOW
   | functions;
```

Would incorrectly parse as "showfunctions" and throw an error.

This fixes the behavior and adds a test for multi-line commands.

Resolves elastic/x-pack-elasticsearch#3410

Original commit: elastic/x-pack-elasticsearch@3870924ccd

qa/sql/src/main/java/org/elasticsearch/xpack/qa/sql/cli/RemoteCli.java

@@ -8,6 +8,7 @@ package org.elasticsearch.xpack.qa.sql.cli;
 import org.apache.logging.log4j.Logger;
 import org.elasticsearch.SpecialPermission;
 import org.elasticsearch.common.Nullable;
+import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.logging.Loggers;
 
 import java.io.BufferedReader;
@@ -23,6 +24,7 @@ import java.nio.charset.StandardCharsets;
 import java.security.AccessController;
 import java.security.PrivilegedAction;
 import java.util.ArrayList;
+import java.util.Iterator;
 import java.util.List;
 import java.util.function.Predicate;
 
@@ -161,7 +163,8 @@ public class RemoteCli implements Closeable {
          * terminal in unix mode to make the tests consistent. */
         out.print(command + ";\n");
         out.flush();
-        String firstResponse = "[?1h=[33msql> [0m" + command + ";";
+        final String firstResponse = "[?1h=[33msql> [0m" +
+                Strings.collectionToDelimitedString(Strings.splitSmart(command, "\n", false), "[?1h=[33m   | [0m") + ";";
         String firstLine = readLine();
         assertThat(firstLine, startsWith(firstResponse));
         return firstLine.substring(firstResponse.length());

qa/sql/src/main/java/org/elasticsearch/xpack/qa/sql/cli/SelectTestCase.java

@@ -19,6 +19,13 @@ public abstract class SelectTestCase extends CliIntegrationTestCase {
         assertThat(readLine(), containsString("test_value"));
         assertEquals("", readLine());
     }
+    public void testMultiLineSelect() throws IOException {
+        index("test", body -> body.field("test_field", "test_value"));
+        assertThat(command("SELECT *\nFROM\ntest"), containsString("test_field"));
+        assertThat(readLine(), containsString("----------"));
+        assertThat(readLine(), containsString("test_value"));
+        assertEquals("", readLine());
+    }
 
     public void testSelectWithWhere() throws IOException {
         index("test", body -> body.field("test_field", "test_value1").field("i", 1));

sql/cli/src/main/java/org/elasticsearch/xpack/sql/cli/CliRepl.java

@@ -40,8 +40,8 @@ public class CliRepl {
             line = line.trim();
 
             if (!line.endsWith(";")) {
-                multiLine.append(" ");
                 multiLine.append(line);
+                multiLine.append(" ");
                 prompt = MULTI_LINE_PROMPT;
                 continue;
             }