Add ability to override log_level at job level

[godber]

The logging level of the teraslice master and all other components is currently controlled in the master configuration using the log_level:

https://terascope.github.io/teraslice/docs/configuration/overview#terafoundation-configuration-reference

It should be possible to specify the log_level (with the same set of options) on the Teraslice job and have that setting override the global setting.

[godber]

This capability should be in https://github.com/terascope/teraslice/releases/tag/v0.90.0