This patch enables a new feature in jmeter plugin: based on the percentage
error, the build is set to unstable or failure.

The new feature is enabled setting two new parameters in the job configuration's
page: errorUnstableThreshold and errorFailedThreshold. By default, these values
are set to zero which means do not change the build status even in the presence
of errors.

This patch also makes the plugin recollect and display jmeter statistics in
failed builds. This is useful in jobs which uses several plugins and when jmeter
information is available although the build was incomplete.

Finally, the patch updates three lines which were using deprecated code.

Thanks
Manolo Carrasco Moñino