Is your feature request related to a problem? Please describe.
If an alternate location for a tool is already defined (e.g. "go.alternateTools": { "gometalinter": "/usr/local/bin/golangci-lint" }) the Install/Update Tools command will still install the same command at another location.

Describe the solution you'd like
When such an alternate definition is already in place for any tool, Install/Update Tools should skip said tool.

Additional context
In my own circumstance, I also have "go.toolsGopath": "~/vscode-go" set, to reduce clutter by keeping VSCode's tools out of my ~/go/bin directory.