Don't swallow exceptions in GlueJob class

[xoen]

Exceptions are a value source of information that can be used to debug problems. By silencing them, the end user (the writer of the Glue Job) will not be able to understand if something went wrong or the job succeeded and will not know what was the cause of the problem: Was it a connectivity issue? was it a credentials problems? was it a quota problem? who knows, it's hard to tell without a stacktrace.

I've added two exception classes:

• JobMisconfigured for when the user didn't set the job_name
• JobNotStarted for when the user tried to get the status of the job but the job doesn't have a run_id (possibly because the user didn't start the job yet

This is just a starting point, we may want to handle some exceptions and add more exceptions classes but it's a good start I think.

Also, I've removed some of the instanceof checks as type checking is often an antipattern. In this specific case we were expecting a dictionary but if that's not the case it means something went wrong before, so there should be an exception (unless we know how to handle it properly, and pass is just silencing a problem).

NOTE: This may potentially break the client code.

[codecov-io]

Codecov Report

Merging #47 into master will increase coverage by 1.5%. The diff coverage is 33.33%.

@@            Coverage Diff            @@
##           master      #47     +/-   ##
=========================================
+ Coverage   72.55%   74.06%   +1.5%     
=========================================
  Files           4        4             
  Lines         809      798     -11     
=========================================
+ Hits          587      591      +4     
+ Misses        222      207     -15

Impacted Files	Coverage Δ
etl_manager/etl.py	58.01% <33.33%> (+4.65%)	:arrow_up:

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[xoen]

Let's double check with out Python ninja @r4vi if this makes sense to him :)

[isichei]

fixes #45