Use new QLibraryInfo::build() in testlib to log build information.

This produces:

********* Start testing of tst_QtJson *********
Config: Using QtTest library 5.3.0, Qt 5.3.0 (Feb 13 2014, GCC 4.6.3, 64 bit, debug build)
PASS : tst_QtJson::initTestCase()

<?xml version="1.0" encoding="UTF-8"?>
<TestCase name="tst_QtJson">
<Environment>
<QtVersion>5.3.0</QtVersion>
<QtBuild>Qt 5.3.0 (Feb 13 2014, GCC 4.6.3, 64 bit, debug build)</QtBuild>
<QTestVersion>5.3.0</QTestVersion>
</Environment>

<?xml version="1.0" encoding="UTF-8" ?>
<testsuite errors="1" failures="1" tests="42" name="tst_QtJson">
<properties>
<property value="5.3.0" name="QTestVersion"/>
<property value="5.3.0" name="QtVersion"/>
<property value="Qt 5.3.0 (Feb 13 2014, GCC 4.6.3, 64 bit, debug build)" name="QtBuild"/>
</properties>

<Environment>
<QtVersion>5.3.0</QtVersion>
<QtBuild>Qt 5.3.0 (Feb 13 2014, GCC 4.6.3, 64 bit, debug build)</QtBuild>
<QTestVersion>5.3.0</QTestVersion>
</Environment>

[ChangeLog][QtTest] Tests now output build information.

Change-Id: I0ab473371575f2b807db725256805b8bffea3454
Reviewed-by: Sergio Ahumada <sahumada@blackberry.com>
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>