Allow Tez task speculation to grant greater customization of certain parameters

Many of the settings for Tez task speculation are hardcoded and should instead be configurable. For example, there's no equivalent config settings for the following MapReduce settings:

• mapreduce.job.speculative.speculative-cap-running-tasks
• mapreduce.job.speculative.retry-after-no-speculate
• mapreduce.job.speculative.retry-after-speculate
• mapreduce.job.speculative.minimum-allowed-tasks
• mapreduce.job.speculative.speculative-cap-total-tasks