Fix process kill bug
Summary:
The workbench can unpredictably crash when the process is attempted to be killed before it has properly spawned/forked. There could be more than one way to identify & fix this condition. This diff proposes to place new process in a new group while instantiating and calls itksysProcess_Interrupt instead of itksysProcess_Kill.
Ref: T29363
Test Plan: NA
Reviewers: floca, O1 MITK Reviewer Group I, kislinsk
Reviewed By: O1 MITK Reviewer Group I, kislinsk
Subscribers: kislinsk
Differential Revision: https://phabricator.mitk.org/D741