allow setting of jobsubmissiondirectory

this is added as optional parameter, if the parameter is not set, then we will use the one created by yarnsubmissionhandler based on application id. if user sets it, user must guarantee its uniqueness across multiple jobs.
this is kind of hairy, anyone knows a better way to find if a optional parameter is bound in a config? if not, i will probably add some helper config.isBound() method in Tang.