Improve the error message of setting cgroup memory limit.

[hetong07]

Fix #10519.

Improve the error message of setting cgroup memory limit. Only provide user-facing warning when '--memory' flag is supplied.

Before PR:

$ minikube start [--memory=4096]
😄  minikube v1.17.1 on Debian rodete
✨  Automatically selected the docker driver
👍  Starting control plane node minikube in cluster minikube
🔥  Creating docker container (CPUs=2, Memory=15900MB) ...
❗  Cgroup v2 does not allow setting memory, if you want to set memory, please modify your Grub as instructed in https://docs.docker.com/engine/install/linux-postinstall/#your-kernel-does-not-support-cgroup-swap-limit-capabilities
🐳  Preparing Kubernetes v1.20.2 on Docker 20.10.3 ...
    ▪ Generating certificates and keys ...
    ▪ Booting up control plane ...
    ▪ Configuring RBAC rules ...
🔎  Verifying Kubernetes components...
    ▪ Using image gcr.io/k8s-minikube/storage-provisioner:v4
🌟  Enabled addons: storage-provisioner, default-storageclass
🏄  Done! kubectl is now configured to use "minikube" cluster and "default" namespace by default

After PR:

$ minikube start
😄  minikube v1.17.1 on Debian rodete
✨  Automatically selected the docker driver
👍  Starting control plane node minikube in cluster minikube
🔥  Creating docker container (CPUs=2, Memory=15900MB) ...
🐳  Preparing Kubernetes v1.20.2 on Docker 20.10.3 ...
    ▪ Generating certificates and keys ...
    ▪ Booting up control plane ...
    ▪ Configuring RBAC rules ...
🔎  Verifying Kubernetes components...
    ▪ Using image gcr.io/k8s-minikube/storage-provisioner:v4
🌟  Enabled addons: storage-provisioner, default-storageclass
🏄  Done! kubectl is now configured to use "minikube" cluster and "default" namespace by default

$ minikube start --memory=4096
😄  minikube v1.17.1 on Debian rodete
✨  Automatically selected the docker driver
❗  Your cgroup does not allow setting memory.
    ▪ More information: https://docs.doInfo.com/engine/install/linux-postinstall/#your-kernel-does-not-support-cgroup-swap-limit-capabilities
👍  Starting control plane node minikube in cluster minikube
🔥  Creating docker container (CPUs=2, Memory=4096MB) ...
🐳  Preparing Kubernetes v1.20.2 on Docker 20.10.3 ...
    ▪ Generating certificates and keys ...
    ▪ Booting up control plane ...
    ▪ Configuring RBAC rules ...
🔎  Verifying Kubernetes components...
    ▪ Using image gcr.io/k8s-minikube/storage-provisioner:v4
🌟  Enabled addons: storage-provisioner, default-storageclass
🏄  Done! kubectl is now configured to use "minikube" cluster and "default" namespace by default

[k8s-ci-robot]

Hi @hetong07. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: hetong07
To complete the pull request process, please assign tstromberg after the PR has been reviewed.
You can assign the PR to them by writing /assign @tstromberg in a comment when ready.

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[minikube-bot]

Can one of the admins verify this patch?

[medyagh]

/ok-to-test