Remove duplication in Mesos schedulers

Currently coarse-grained and fine-grained Mesos schedulers don't share much code, and that leads to inconsistencies. For instance:

• only coarse-grained mode respects spark.cores.max, see SPARK-9873
• only coarse-grained mode blacklists slaves that fail repeatedly, but that seams like generally useful
• constraints and memory checking are done on both sides (code is shared though)
• framework re-registration (master election) is only done for cluster-mode deployment

We should find a better design that groups together common concerns and generally improves the code.