Resolve "bbctl add more k3d tests"

General MR

Summary

Add tests for the k3d operations previously added to BBCTL.

Relevant logs/screenshots

Increase K3D command test coverage from 53.3% on the main brach to 100.0% on the 110-add-more-test branch

bbctl (main) ✗ go test './cmd/k3d' -v --coverprofile=cover.txt
...
 --- PASS: TestK3d_NewHostsCmd_Run (0.00s)
PASS
coverage: 53.3% of statements
ok  	repo1.dso.mil/big-bang/product/packages/bbctl/cmd/k3d	1.474s	coverage: 53.3% of statements

vs.

bbctl (110-add-more-test) ✗ go test './cmd/k3d' -v --coverprofile=cover.txt
...
--- PASS: TestK3d_SshBadArgs (0.05s)
PASS
coverage: 100.0% of statements
ok  	repo1.dso.mil/big-bang/product/packages/bbctl/cmd/k3d	1.527s	coverage: 100.0% of statements

Linked Issue

#110 (closed)

Upgrade Notices

N/A

Closes #110 (closed)