check walltime of glidein

[dsschult]

Some clusters have noticed that glideins are going over the walltime limit. Make sure that the maximum walltime includes the retirement time, so the glidein dies when requested.

Probably also try to die a few minutes before then, so hard kill clusters don't hit the limit.

[dsschult]

@claudiok also asked that we set the retirement time much earlier, say 1/2 the walltime or 4 hours after start. This would help fix the problem of jobs hitting the max walltime.