fix: registry check strips port

[emosbaugh]

What this PR does / why we need it:

Fixes an issue:

kubectl kots install ethan-kots/unstable \
  --namespace default \
  --airgap-bundle ~/Downloads/ethan-kots-0.1.207.airgap \
  --license-file ~/Downloads/ethan-kots-unstable.yaml \
  --shared-password admin123 \
  --kotsadm-registry 127.0.0.1:6443
  • Validating registry information ✗  
Error: Failed to test access to "127.0.0.1" with user "": failed to ping registry: Get "http://127.0.0.1/v2/": dial tcp 127.0.0.1:80: connect: connection refused

After fix:

./bin/kots install ethan-kots/unstable \
  --namespace default \
  --airgap-bundle ~/Downloads/ethan-kots-0.1.207.airgap \
  --license-file ~/Downloads/ethan-kots-unstable.yaml \
  --shared-password admin123 \
  --kotsadm-registry 127.0.0.1:6443
  • Validating registry information ✗  
  • Extracting airgap bundle
Extracting /var/folders/k4/ntyttg4s6r77y6wxvrmm27_h0000gn/T/kotsadm-airgap2538116769/airgap.yaml
...

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Steps to reproduce

Does this PR introduce a user-facing change?

Fixes an issue that causes the port to be removed from the `--kotsadm-registry` flag, preventing an airgapped installation from succeeding, with an error validating the registry when performing a kots install, upgrade or pushing admin console images.

Does this PR require documentation?