Revert "fix(coreos): tune etcd to address high disk i/o environments"

In testing, this commit causes more harm than good, and
results in etcd/fleet going haywire.

This reverts commit 4f95cb82c87e75c6492ce0084961d57b0d70ae31.
Merge pull request #2663 from carmstrong/revert-etcd_timeout

Revert "fix(coreos): tune etcd to address high disk i/o environments"