Update temporary directory usage in tests

[edaniszewski]

Instead of using the custom temporary directory fixtures set up long ago, this updates tests to use pytest's tmpdir. Since socket names have a character limit (I think something like 100 chars), and tmpdir tends to make long/nested directories (good for isolation, bad for this use case), a tmpsocket fixture was created to manage sockets for tests.

[codecov]

Codecov Report

Merging #233 into jenkins-ci will increase coverage by 0.07%.
The diff coverage is n/a.

@@              Coverage Diff               @@
##           jenkins-ci     #233      +/-   ##
==============================================
+ Coverage       87.76%   87.83%   +0.07%     
==============================================
  Files              46       46              
  Lines            1381     1381              
==============================================
+ Hits             1212     1213       +1     
+ Misses            169      168       -1

Impacted Files	Coverage Δ
synse/plugin.py	88.59% <0%> (+0.67%)	⬆️

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