[BEAM-889] CheckpointDir option does not accept relative path and req…

[amitsela]

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…uires protocol.

[amitsela]

This seems much more friendly (and less code!).

Spark already does it's due-diligence on the provided checkpoint dir so no need to double verify.
Still warn if prefix does not much a reliable storage.

[amitsela]

Jenkins failed on Dataflow IT test, unrelated.

[amitsela]

R: @tgroh

[amitsela]

R: @jbonofre if you're available ;-)

[jbonofre]

Sure ! Thanks !

[tgroh]

The commit message doesn't seem to match the actual change, which is basically "handle relative paths in Spark CheckpointDir"

other than that, LGTM.

[amitsela]

@tgroh it describes the issue instead of the solution.. mostly to match the ticket.
I'll change the commit message (leaving the ticket id) as it does make more sense.
Thanks!

[jbonofre]

LGTM