Storing parsed JMeter report results into xml file

After parsing the JMeter reports, the results are stored into a xml
file that is stored as an artifact of the build.

- For the error threshold calculation, the xml file contains response
times information.

- For the build comparison, the xml file contains the comparison
results between two builds and response times information. (comparison
works for single jmeter files)
Merge pull request #22 from palvinds/master

Storing parsed JMeter report results into xml file