Can't save and exit when test plans have prometheus elements

[johrstrom]

For whatever reason, this plugin is holding up the exit routine for JMeter when Saving then exiting.

To replicate simply:
load plugin version 0.2.0-rc1 into prometheus
open the example testplan in docs/examples
close jmeter, and when prompted to save, click yes

Expected results: jmeter saves and exists
actual results: jmeter saves but does not exit.

[johrstrom]

As a work around one can simply load any other test plan or start a new one and exit cleanly.

[johrstrom]

Fixed in 0.2.0-rc2.