use same etcd data directory regardless of version

This introduces a known issue next deploy, but prevents it from happening
every time we upgrade the etcd version. The fix is to stop all etcds, blow
away their data directories, and start them again.

[finishes #66790592]

Signed-off-by: Alex Suraci <asuraci@pivotallabs.com>
Merge remote-tracking branch 'origin/pr/328' into develop