Add a junit format to run-tests.sh

The patch adds a new output format for run-tests.sh that is actually useful when parsed by jenkins and the junit plugin. It builds on what drupalci does and the drush patch.

php scripts/run-tests.sh --url http://localhost/ --junit tests Session

gives something like:

<?xml version="1.0" encoding="UTF-8"?>
<testsuite tests="151" disabled="0" errors="11" failures="45">
  <testcase name="setUp()" assertions="2" classname="Session.Session HTTPS handling" status="pass">
    <system-out><![CDATA[pass:      [Other] Enabled modules: session_test [session.test:304]
pass:      [Other] Enabled modules: session_test [session.test:304]
]]></system-out>
  </testcase>
  <testcase name="testHttpsSession()" assertions="123" classname="Session.Session HTTPS handling" status="failed">
    <failure type="fail" message="Number of failed assertions: 35"><![CDATA[fail:      [Other] Failed to set field name to htF3iJoI [session.test:327]
…]]></failure>
    <error type="exception" message="Number of unexpected errors: 11"><![CDATA[exception: [Notice] Undefined index: SSESS49960de5880e8c687434170f6476605b [session.test:337]
…]]></error>
    <system-out><![CDATA[pass:      [Role] Created role of name: aum4bHeD, id: 4 [session.test:319]
…]]></system-out>
  </testcase>
  <testcase name="simpletest_script_run_one_test()" assertions="2" classname="Session.Session HTTPS handling" status="failed">
    <failure type="fail" message="Number of failed assertions: 2"><![CDATA[fail:      [Other] Failed to find test tables to drop. [run-tests.php:395]
fail:      [Other] Failed to find test tables to drop. [run-tests.php:395]
]]></failure>
    <system-out><![CDATA[fail:      [Other] Failed to find test tables to drop. [run-tests.php:395]
fail:      [Other] Failed to find test tables to drop. [run-tests.php:395]
]]></system-out>
  </testcase>
  <testcase name="testEmptySessionId()" assertions="25" classname="Session.Session HTTPS handling" status="failed">
    <failure type="fail" message="Number of failed assertions: 8"><![CDATA[fail:      [Other] Failed to set field name to pYgID2r7 [session.test:509]
…]]></failure>
    <system-out><![CDATA[pass:      [Role] Created role of name: w2Ta0jei, id: 4 [session.test:496]
…]]></system-out>
  </testcase>
</testsuite>