cmd/go/internal/modfetch/codehost: quote arguments to commands printed from -x
cmd/go/internal/modfetch/codehost: quote arguments to commands printed from -x

Some of the arguments — particularly format strings passed to git commands — may
contain spaces, and it's useful to be able to paste commands from 'go get -x
foo' directly into a shell to reproduce their output.

Change-Id: I4f0c0b4e05db8b5232458e9a271f2ccbb665e85a
Reviewed-on: https://go-review.googlesource.com/126955
Run-TryBot: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

nawawi/go,cloudflare/go,nawawi/go,cloudflare/go,nawawi/go,golang/go,cloudflare/go,nawawi/go,cloudflare/go,cloudflare/go,akutz/go,golang/go,CAFxX/go,cloudflare/go,nawawi/go,josharian/go,golang/go,josharian/go,CAFxX/go,josharian/go,CAFxX/go,CAFxX/go,golang/go,CAFxX/go,josharian/go,josharian/go,golang/go,CAFxX/go,akutz/go,golang/go,cloudflare/go,CAFxX/go,golang/go,akutz/go,akutz/go,akutz/go,josharian/go,cloudflare/go,akutz/go,josharian/go,golang/go,nawawi/go,akutz/go,akutz/go,nawawi/go,josharian/go,CAFxX/go,nawawi/go