adding unit tests, pt. 2

[edaniszewski]

This PR adds a bunch of unit tests, does some cleanup, and fixes some bugs found as a result of the tests. There is more work to be done, but opening this PR to try and keep the size manageable at least.

The primary work here is in the sub-packages where we will have pretty good coverage.

ok  	github.com/vapor-ware/synse-sdk/sdk	1.053s	coverage: 14.3% of statements
ok  	github.com/vapor-ware/synse-sdk/sdk/config	1.058s	coverage: 94.8% of statements
ok  	github.com/vapor-ware/synse-sdk/sdk/errors	1.031s	coverage: 100.0% of statements
ok  	github.com/vapor-ware/synse-sdk/sdk/health	1.040s	coverage: 77.0% of statements
ok  	github.com/vapor-ware/synse-sdk/sdk/output	1.037s	coverage: 100.0% of statements
ok  	github.com/vapor-ware/synse-sdk/sdk/policy	1.034s	coverage: 100.0% of statements
ok  	github.com/vapor-ware/synse-sdk/sdk/scripts	1.049s	coverage: 100.0% of statements
ok  	github.com/vapor-ware/synse-sdk/sdk/utils	1.036s	coverage: 100.0% of statements

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (v3/staging@ef98501). Click here to learn what that means.
The diff coverage is 100%.

@@              Coverage Diff              @@
##             v3/staging     #383   +/-   ##
=============================================
  Coverage              ?   41.33%           
=============================================
  Files                 ?       35           
  Lines                 ?     2269           
  Branches              ?        0           
=============================================
  Hits                  ?      938           
  Misses                ?     1312           
  Partials              ?       19

Impacted Files	Coverage Δ
sdk/output/reading.go	100% <100%> (ø)
sdk/health/periodic.go	85.29% <100%> (ø)
sdk/config/plugin.go	100% <100%> (ø)
sdk/health/manager.go	72% <100%> (ø)
sdk/output/output.go	100% <100%> (ø)
sdk/tag.go	53.89% <100%> (ø)

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