Implement config knob STARTER_DEFAULT_JOB_HOOK_KEYWORD. HTCONDOR-1400
Implement config knob STARTER_DEFAULT_JOB_HOOK_KEYWORD. HTCONDOR-1400

This knob allows the EP to specify a default starter job hook in
the case that the job does not specify a vaild hook.

htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor