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"