Clean up zombie processes on backup failure

Ensure that a SIGTERM is sent to the session leader of the process
group, so that all backup processes are terminated in case of a
FAILURE. This ensures that no zombie processes are left behind.

Closes bug 1253850

Change-Id: I4bd53c37923f83abe4c51deb95d740656ab21979
Added ability to pass custom command-line options to backup runner

Added a new DictOpt field "backup_runner_options" to the trove config
Custom command-line options for the backup runner can be passed in
through this

Closes-Bug: 1253849

Change-Id: I2ea45aa4899da4126776ef14a9cb2f0328a9e544
Merge "Added ability to pass custom command-line options to backup runner"
Merge "Clean up zombie processes on backup failure"