Multiple fixes for stability

 - Adding option to prevent rollback in case of successful execution of a destructive operation that is not reversible (deleting gear or deconfiguring cartridge on the node)
 - Checking for the existence of the application after obtaining the lock
 - Reloading the application after acquiring the lock to reflect any changes made by the previous operation holding the lock
 - Using regular run_jobs code in clear-pending-ops script
 - Handling DocumentNotFound exception in clear-pending-ops script if the application is deleted