Fix panic on rootless build without push

[dhiltgen]

Some recent UX refinements broke the rootless creation flow.
Also a miswired error case resulted in a nil error
when there should have been an error which led to the panic.
Enabled and refined the integration tests for rootless coverage.

Closes #32

[codecov-io]

Codecov Report

Merging #56 (e8db8fc) into main (3821ca0) will increase coverage by 2.52%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #56      +/-   ##
==========================================
+ Coverage   50.30%   52.83%   +2.52%     
==========================================
  Files          38       38              
  Lines        2465     2491      +26     
==========================================
+ Hits         1240     1316      +76     
+ Misses       1073     1020      -53     
- Partials      152      155       +3     

Flag	Coverage Δ
integration-tests	52.31% <100.00%> (+2.54%)	⬆️
unit-tests	4.41% <0.00%> (-0.05%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
integration/common/basesuites.go	100.00% <100.00%> (ø)
pkg/build/build.go	27.12% <100.00%> (+1.29%)	⬆️
pkg/cmd/create.go	74.19% <100.00%> (ø)
pkg/driver/kubernetes/factory.go	69.12% <100.00%> (-1.15%)	⬇️
pkg/driver/kubernetes/driver.go	63.56% <0.00%> (+2.71%)	⬆️
pkg/driver/kubernetes/execconn/execconn.go	90.90% <0.00%> (+3.03%)	⬆️
pkg/driver/kubernetes/manifest/manifest.go	97.37% <0.00%> (+4.80%)	⬆️
pkg/build/output.go	41.17% <0.00%> (+36.76%)	⬆️

---

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 e7d2ca3...e8db8fc. Read the comment docs.