SPARK-4338. Ditch yarn-alpha.

Sorry if this is a little premature with 1.2 still not out the door, but it will make other work like SPARK-4136 and SPARK-2089 a lot easier.
I know you didn't change this here (so we can file separate jira for it if you want) but perhaps we should add example and some text here about hadoop 2.5 and >.   Since there is no hadoop profile 2.5 and the user should use the 2.4 profile.