Bug#19535 mysql-test-run cannot handle crashing test cases

- Make mysql-test-run.pl restart a crashed/stopped process if it was expected it should crash.
 - Added testcase for "crash_commit_before", which tests behaviour when server crashes just before commit.
  * The testcase first write a small var/tmp/master0.expect file indicating expected crash
  * Then sets "DEBUG" variable to for example "d,crash_commit_before" and then executes a commit.
  * The server will crash and be brought back up by mysql-test-run.pl
  * Test case will then wait for the process to come back online before continuing.

mysql-test/include/wait_until_connected_again.inc

@@ -0,0 +1,20 @@
+#
+# Include this script to wait until the connection to the
+# server has been restored or timeout occurs
+--disable_result_log
+--disable_query_log
+let $counter= 100;
+while ($mysql_errno)
+{
+  --error 0,2002,2006
+  show status;
+
+  dec $counter;
+  if (!$counter)
+  {
+    --die Server failed to restart
+  }
+  --sleep 0.1
+}
+--enable_query_log
+--enable_result_log