Operator: doOnTerminate

Like finallyDo but before emitting the terminal state instead of after.
Merge pull request #918 from benjchristensen/doOnTerminate

Operator: doOnTerminate
Added additional test to prove issue
BugFix: Zip with 0 Observables

Fixes bug reported at https://github.com/Netflix/RxJava/pull/868
Merge pull request #919 from benjchristensen/zip-bugfix-868

BugFix: Zip Never Completes When Zero Observables
Delete Deprecated onSubscribeStart That Doesn't Work

- It's messy to make this work so deleting it instead.
- Better to move forward in the 0.17 release than try and make this work for the very small percentage (probably only Netflix) that uses it.
Merge pull request #920 from benjchristensen/delete-deprecated-hook-method

Delete Deprecated onSubscribeStart That Doesn't Work
[Gradle Release Plugin] - pre tag commit:  '0.17.0-RC4'.
[Gradle Release Plugin] - new version commit:  '0.17.0-RC5-SNAPSHOT'.