builder: remove container package dependency

Signed-off-by: Tibor Vass <tibor@docker.com>

system/path_unix.go

@@ -0,0 +1,8 @@
+// +build !windows
+
+package system
+
+// DefaultPathEnv is unix style list of directories to search for
+// executables. Each directory is separated from the next by a colon
+// ':' character .
+const DefaultPathEnv = "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"

system/path_windows.go

@@ -0,0 +1,7 @@
+// +build windows
+
+package system
+
+// DefaultPathEnv is deliberately empty on Windows as the default path will be set by
+// the container. Docker has no context of what the default path should be.
+const DefaultPathEnv = ""