move platform specific code to dedicated platform files

pkg/commands/os_default_platform.go

@@ -0,0 +1,16 @@
+// +build !windows
+
+package commands
+
+import (
+	"runtime"
+)
+
+func getPlatform() *Platform {
+	return &Platform{
+		os:           runtime.GOOS,
+		shell:        "bash",
+		shellArg:     "-c",
+		escapedQuote: "\"",
+	}
+}