Revert "[maven-release-plugin] prepare for next development iteration"

This reverts commit 34aa342138a06913787ab1cec7ee7b57a14f7cba.
Revert "[maven-release-plugin] prepare release v0.8.0-incubating"

This reverts commit d9e80d53f6535f022ca59e11ffd1d164c17548d9.
Make spark-kafka a "provided" dependency.

Otherwise any third-party build that links against spark-streaming
will break (even if they aren't using kafka). This also defines the
local repository inside of the examples pom so that the examples
build continues to work.