Use build_context when building image for recorded run

[craig-willis]

Fixes whole-tale/whole-tale#126

Test case:

• Assumes image has never been built
• Create tale from https://github.com/whole-tale/rrun-test
• Start recorded run without first building image via Run Tale or Build Image
• Confirm that image is built, pushed, and run succeeds.

[codecov]

Codecov Report

Base: 72.00% // Head: 71.74% // Decreases project coverage by -0.25% ⚠️

Coverage data is based on head (74dad81) compared to base (c516e49).
Patch coverage: 25.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #188      +/-   ##
==========================================
- Coverage   72.00%   71.74%   -0.26%     
==========================================
  Files          11       11              
  Lines        1536     1529       -7     
==========================================
- Hits         1106     1097       -9     
- Misses        430      432       +2     

Impacted Files	Coverage Δ
gwvolman/tasks.py	55.81% <0.00%> (-1.16%)	⬇️
gwvolman/build_utils.py	91.66% <100.00%> (+0.06%)	⬆️

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