Update test fixtures and plugin utils

[cgewecke]

• Generalizes plugin utilities path key names
• Puts truffle specific plugin utilities in their own file
• Adds buidler.config.js to all the test fixtures, projects
• Rewrites tests to avoid contract.deployed()
• Skips the oraclize instrumentation speed test because length of compilation is annoying.

[codecov-io]

Codecov Report

Merging #422 into buidler-plugin will increase coverage by 0.01%.
The diff coverage is 100%.

@@                Coverage Diff                 @@
##           buidler-plugin     #422      +/-   ##
==================================================
+ Coverage           99.06%   99.07%   +0.01%     
==================================================
  Files                  14       15       +1     
  Lines                 639      649      +10     
==================================================
+ Hits                  633      643      +10     
  Misses                  6        6

Impacted Files	Coverage Δ
lib/validator.js	100% <ø> (ø)	⬆️
dist/plugin-assets/plugin.utils.js	97.22% <100%> (-1.27%)	⬇️
dist/truffle.plugin.js	100% <100%> (ø)	⬆️
dist/plugin-assets/truffle.utils.js	100% <100%> (ø)

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