Do not detect as a remote run if DOCKER_HOST is set to a unix:// socket

[jacob733]

Certain use cases set DOCKER_HOST even if it points to a local docker instance. So a simple check if the variable is set is insufficient in some cases. Adding a check for if the variable is set to something using the unix:// protocol will make this filter more exact.

[codecov-io]

Codecov Report

Merging #99 into master will decrease coverage by 0.39%.
The diff coverage is 50%.

@@            Coverage Diff            @@
##           master      #99     +/-   ##
=========================================
- Coverage   97.08%   96.68%   -0.4%     
=========================================
  Files           9        9             
  Lines         480      483      +3     
=========================================
+ Hits          466      467      +1     
- Misses         14       16      +2

Impacted Files	Coverage Δ
scuba/__main__.py	96.46% <50%> (-0.85%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a88c699...ddbe140. Read the comment docs.

[JonathonReinhart]

This looks good to me. For my own curiosity, would you mind elaborating on the use cases which set DOCKER_HOST even on a local Docker instance?

[jacob733]

For my case, it is for use with Jenkins, where an explicit DOCKER_HOST setting provides for a more readable configuration.

Note that if DOCKER_HOST is set to something like tcp://127.0.0.1... then this will still not be detected as a local docker. This is because such a setting might just as well be pointing to a local SSH port forward, which is one way to safely connect to a remote docker daemon.