Bring -e|--env args in line with docker

[timvisher]

Closes #473

This closes the gap between how docker run -e|--env and circleci local execute -e|--env behaves. Now, as in docker run, bare -e|--env VAR arguments are resolved from the local environment and passed on to picard properly. Arguments that are fully specified are never resolved from the environment and arguments are still required to be passed in order to forward them on to picard (i.e. there isn't any automatic inclusion of the environment in the picard arguments).

I'm happy to spin out the Vagrantfile if that's not welcome just yet but rather than figuring out to get Docker for Mac and golang set up on my MacBook I figured I'd just make an environment that anyone can benefit from.

Obviously I'd like to clean up the commits prior to merge but I wanted to get the discussion going.

[codecov]

Codecov Report

Merging #487 into master will decrease coverage by 0.01%.
The diff coverage is 40.00%.

@@            Coverage Diff             @@
##           master     #487      +/-   ##
==========================================
- Coverage   26.84%   26.82%   -0.02%     
==========================================
  Files          35       35              
  Lines        4739     4764      +25     
==========================================
+ Hits         1272     1278       +6     
- Misses       3341     3356      +15     
- Partials      126      130       +4     

Impacted Files	Coverage Δ
local/local.go	36.92% <40.00%> (-1.50%)	⬇️

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[timvisher]

Let me know whether there's interest in merging this and I'll try to fix up the code coverage.

[timvisher]

Ping. :)

[timvisher]

Ping on this. :)