Configure Spark client timeouts using Hadoop time durations

[arielshaqed]

Instead of hand-crafted parsing routines, use Hadoop Configuration.getTimeDuration for our timeouts.

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[arielshaqed]

@ozkatz probably useful before a possible "1.0" release. (This is Spark metadata client, mind. lakeFSFS is different because it lives in the Hadoop ecosystem where raw numbers rule...)