Feature to parse custom fields from Junit.xml and update in TestLink

[mazimkhan]

This PR adds a feature to read execution time custom field values from the JUnit.xml file and update the test results with them.
Example of JUnit.xml:

<?xml version="1.0" encoding="UTF-8"?>
<testsuite failures="0" tests="6" errors="1" time="0.149999856949">
    <testcase classname="FLASH_SET_test_01_start" name="FLASH_SET_test_01_start" time="0.0499999523163">
        <host_os>Windows</host_os>
        <power>0.5</power>
        <error>
    </testcase>
    <testcase classname="FLASH_SET_test_01_start" name="FLASH_SET_test_01_start" time="0.0499999523163">
        <host_os>Windows</host_os>
        <power>0.6</power>
    </testcase>
    <testcase classname="FLASH_SET_test_01_start" name="FLASH_SET_test_01_start" time="0.0499999523163">
        <host_os>Windows</host_os>
        <power>0.5</power>
    </testcase>
</testsuite>