Provide unique error code (GUEST_KIC_CP_PUBKEY) for not copyable cert for kic

[medyagh]

helps with breaking down #9907
and proivdes a lil better advice for #10772

Before this PR

make: `out/minikube' is up to date.
😄  minikube v1.18.1 on Darwin 11.2.3
✨  Using the docker driver based on user configuration
👍  Starting control plane node minikube in cluster minikube
🔥  Creating docker container (CPUs=2, Memory=4000MB) ...
✋  Stopping node "minikube"  ...
🛑  Powering off "minikube" via SSH ...
🔥  Deleting "minikube" in docker ...
🤦  StartHost failed, but will try again: creating host: create: creating: prepare kic ssh: copying pub key: docker copy /var/folders/s8/wxxccj3x7mncysv_zzm5w_r400h78j/T/tmpf-memory-asset520910982 into minikube:/home/docker/.ssh/authorized_keys, output: lstat /private/var/folders/s8/wxxccj3x7mncysv_zzm5w_r400h78j/T/tmpf-memory-asset520910982: no such file or directory
: exit status 1
🔥  Creating docker container (CPUs=2, Memory=4000MB) ...
😿  Failed to start docker container. Running "minikube delete" may fix it: creating host: create: creating: prepare kic ssh: copying pub key: docker copy /var/folders/s8/wxxccj3x7mncysv_zzm5w_r400h78j/T/tmpf-memory-asset368501293 into minikube:/home/docker/.ssh/authorized_keys, output: lstat /private/var/folders/s8/wxxccj3x7mncysv_zzm5w_r400h78j/T/tmpf-memory-asset368501293: no such file or directory
: exit status 1

❌  Exiting due to GUEST_PROVISION: Failed to start host: creating host: create: creating: prepare kic ssh: copying pub key: docker copy /var/folders/s8/wxxccj3x7mncysv_zzm5w_r400h78j/T/tmpf-memory-asset368501293 into minikube:/home/docker/.ssh/authorized_keys, output: lstat /private/var/folders/s8/wxxccj3x7mncysv_zzm5w_r400h78j/T/tmpf-memory-asset368501293: no such file or directory
: exit status 1

😿  If the above advice does not help, please let us know: 
👉  https://github.com/kubernetes/minikube/issues/new/choose

After this PR

$ make && mk start --driver=docker
go build  -tags "" -ldflags="-X k8s.io/minikube/pkg/version.version=v1.18.1 -X k8s.io/minikube/pkg/version.isoVersion=v1.18.0-1615350772-10704 -X k8s.io/minikube/pkg/version.gitCommitID="ff0e25ada888cf1bd7b262857ce96531c1231e69-dirty" -X k8s.io/minikube/pkg/version.storageProvisionerVersion=v4" -o out/minikube k8s.io/minikube/cmd/minikube
😄  minikube v1.18.1 on Darwin 11.2.3
✨  Using the docker driver based on user configuration
👍  Starting control plane node minikube in cluster minikube
🔥  Creating docker container (CPUs=2, Memory=4000MB) ...
✋  Stopping node "minikube"  ...
🛑  Powering off "minikube" via SSH ...
🔥  Deleting "minikube" in docker ...
🤦  StartHost failed, but will try again: creating host: create: creating: prepare kic ssh: copying pub key: docker copy /var/folders/s8/wxxccj3x7mncysv_zzm5w_r400h78j/T/tmpf-memory-asset265183811 into minikube:/home/docker/.ssh/authorized_keys, output: lstat /private/var/folders/s8/wxxccj3x7mncysv_zzm5w_r400h78j/T/tmpf-memory-asset265183811: no such file or directory
: exit status 1
🔥  Creating docker container (CPUs=2, Memory=4000MB) ...
😿  Failed to start docker container. Running "minikube delete" may fix it: creating host: create: creating: prepare kic ssh: copying pub key: docker copy /var/folders/s8/wxxccj3x7mncysv_zzm5w_r400h78j/T/tmpf-memory-asset091998406 into minikube:/home/docker/.ssh/authorized_keys, output: lstat /private/var/folders/s8/wxxccj3x7mncysv_zzm5w_r400h78j/T/tmpf-memory-asset091998406: no such file or directory
: exit status 1

❌  Exiting due to GUEST_KIC_CP_PUBKEY: Failed to start host: creating host: create: creating: prepare kic ssh: copying pub key: docker copy /var/folders/s8/wxxccj3x7mncysv_zzm5w_r400h78j/T/tmpf-memory-asset091998406 into minikube:/home/docker/.ssh/authorized_keys, output: lstat /private/var/folders/s8/wxxccj3x7mncysv_zzm5w_r400h78j/T/tmpf-memory-asset091998406: no such file or directory
: exit status 1
💡  Suggestion: Ensure the tmp directory path is writable to the current user.
🍿  Related issue: https://github.com/kubernetes/minikube/issues/10772

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

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