`gcloud preview --help >/dev/null 2>&1` would silently hang if the
preview component was not installed. Instead, let stderr flow normally.
to reproduce the bug and verify the fix:
1. gcloud components remove preview #answer yes
2. gcloud preview --help >/dev/null 2>&1 #note the hang, ^C
3A. gcloud preview --help >/dev/null #now prompts you to install preview component
the fix also works when run via "kube-up.sh"
alternatively: `gcloud -q preview --help >/dev/null 2>&1` will silently install
the missing preview component
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