Fixing unexpanded CMD variable with correct defaulting behavior.

[ohemmali]

After further testing, defaulting was not correctly occurring. Switching to env var expansion with embedded default value.

[codecov]

Codecov Report

Merging #478 (3f003c8) into development (5427c16) will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           development     #478   +/-   ##
============================================
  Coverage        94.63%   94.63%           
============================================
  Files               35       35           
  Lines             2761     2761           
============================================
  Hits              2613     2613           
  Misses             114      114           
  Partials            34       34           

---

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 5427c16...3f003c8. Read the comment docs.