SseProtocol error handling cleanup

[JayH5]

• Don't log PotentialDataLoss.. doesn't seem to mean much and fills up logs
• Errback on waiting deferreds for unexpected errors

[codecov[bot]]

Codecov Report

Merging #123 into develop will decrease coverage by 0.09%. The diff coverage is 95.83%.

@@            Coverage Diff             @@
##           develop     #123     +/-   ##
==========================================
- Coverage    99.89%   99.79%   -0.1%     
==========================================
  Files           20       20             
  Lines         1954     1983     +29     
  Branches       100      104      +4     
==========================================
+ Hits          1952     1979     +27     
  Misses           1        1             
- Partials         1        3      +2

Impacted Files	Coverage Δ
marathon_acme/tests/test_clients.py	99.77% <100%> (-0.01%)	:arrow_down:
marathon_acme/tests/test_sse_protocol.py	100% <100%> (ø)	:arrow_up:
marathon_acme/sse_protocol.py	100% <100%> (ø)	:arrow_up:
marathon_acme/tests/test_fake_marathon.py	100% <100%> (ø)	:arrow_up:
marathon_acme/service.py	98.29% <81.81%> (-1.71%)	:arrow_down:

[JayH5]

I'm putting this on hold for now as it fixes a minor issue (too much logs), is difficult to test, and introduces a bunch of complexity.