Fix config server testing

[wtgee]

• Config server doesn't parse config as loaded so it doesn't need to serialize it before sending a response. The serialization should happen by the client side get_config.
• Restores the config server testing. Closes #296.
• Explicitly ignores the config server file for coverage even though it should be covered by the threads.

[codecov[bot]]

Codecov Report

Merging #302 (f5d7d7a) into develop (552d78f) will increase coverage by 2.63%. The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop     #302      +/-   ##
===========================================
+ Coverage    91.48%   94.11%   +2.63%     
===========================================
  Files           22       23       +1     
  Lines         1432     1428       -4     
===========================================
+ Hits          1310     1344      +34     
+ Misses         122       84      -38     

Impacted Files	Coverage Δ
src/panoptes/utils/config/client.py	100.00% <ø> (ø)
src/panoptes/utils/config/server.py
src/panoptes/utils/config/cli.py	48.14% <0.00%> (ø)
src/panoptes/utils/config/helpers.py	100.00% <0.00%> (+1.72%)	:arrow_up:

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