Fix run_script method.
Fix run_script method.

Existing code assumes the script sent by the user is terminated with a newline.
Appending magic string without '\n' before print() command results in a syntactically
incorrect Groovy code.
This patch ensures that '\n' is added between user's provided script and appended
magic string.

Change-Id: I39021f1058e7434d487efb4bc7aca18416b2c08e

stackforge/python-jenkins