wasi: makes wasmtime "run" explicit

wasmtime by default will assume the subcommand is "run" vs one of its
others, but being explicit helps clarify the actual command invoked.

For example, we pass similar looking args to wasmtime and also wasi.

Signed-off-by: Adrian Cole <adrian@tetrate.io>

main.go

@@ -285,9 +285,9 @@ func Test(pkgName string, stdout, stderr io.Writer, options *compileopts.Options
 			// relative directory up to the module root, even if the test never
 			// reads any files.
 			//
-			// Ex. --dir=.. --dir=../.. --dir=../../..
+			// Ex. run --dir=.. --dir=../.. --dir=../../..
 			dirs := dirsToModuleRoot(result.MainDir, result.ModuleRoot)
-			var args []string
+			args := []string{"run"}
 			for _, d := range dirs[1:] {
 				args = append(args, "--dir="+d)
 			}