Allow passing only exposed port to --ports

[spowelljr]

Fixes #14731

When port validation was added the case for just passing the port to expose was forgotten and made that possibility impossible.

Before:

$ minikube start --ports 8080
😄  minikube v1.27.0 on Darwin 12.6 (arm64)
✨  Automatically selected the docker driver. Other choices: ssh, qemu2 (experimental)

❌  Exiting due to MK_USAGE: Sorry, one of the ports provided with --ports flag is not valid [8080]

After:

$ minikube start --ports 8080
😄  minikube v1.27.0 on Darwin 12.6 (arm64)
✨  Automatically selected the docker driver. Other choices: ssh, qemu2 (experimental)
📌  Using Docker Desktop driver with root privileges
👍  Starting control plane node minikube in cluster minikube
🚜  Pulling base image ...
🔥  Creating docker container (CPUs=2, Memory=4000MB) ...
🐳  Preparing Kubernetes v1.25.2 on Docker 20.10.18 ...
❌  Unable to load cached images: loading cached images: stat /Users/powellsteven/.minikube/cache/images/arm64/registry.k8s.io/kube-controller-manager_v1.25.2: no such file or directory
    ▪ Generating certificates and keys ...
    ▪ Booting up control plane ...
    ▪ Configuring RBAC rules ...
🔎  Verifying Kubernetes components...
    ▪ Using image gcr.io/k8s-minikube/storage-provisioner:v5
🌟  Enabled addons: default-storageclass
🏄  Done! kubectl is now configured to use "minikube" cluster and "default" namespace by default

$  docker ps --format "{{.Ports}}"
0.0.0.0:64745->22/tcp, 0.0.0.0:64746->2376/tcp, 0.0.0.0:64748->5000/tcp, 0.0.0.0:64749->8080/tcp, 0.0.0.0:64750->8443/tcp, 0.0.0.0:64747->32443/tcp

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This pull-request has been approved by: medyagh, spowelljr

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