Merge pull request #3 from mesos/v4

merge upstream changes
Use pssh.

Replace bash-isms with pssh to neatly parallelize cluster operations.

Also, decrease questionably high sleep times.
Approve key to local hostname.
approve keys twice
time the pssh calls
Revert "time the pssh calls"

This reverts commit d9333af0a21d1aff3216471823344f326ef84cfb.
test removing ssh pre-approval
use pushd/popd
remove unused ssh pre-approval code
sudo yum
Merge pull request #86 from nchammas/use-pssh

[SPARK-4948] Use pssh.