use --ignore-installed instead of --target

Author: NicholasBHubbard

lib/fpm/package/python.rb

@@ -594,14 +594,6 @@ def fix_name(name)
     end
   end # def fix_name
 
-  def pip_install_dir()
-    execmd([attributes[:python_bin], "-c",
-            "import sysconfig; print(sysconfig.get_path('stdlib'))"],
-           :stdin => false, :stderr => false) do |stdout|
-      return stdout.read(64<<10).strip()
-    end
-  end
-
   # Install this package to the staging directory
   def install_to_staging(path)
     prefix = "/"
@@ -610,8 +602,10 @@ def install_to_staging(path)
     # XXX: Note: pip doesn't seem to have any equivalent to `--install-lib` or similar flags.
     # XXX: Deprecate :python_install_data, :python_install_lib, :python_install_bin
     # XXX: Deprecate: :python_setup_py_arguments
-    flags = [ "--target", staging_path + pip_install_dir() ]
-    #flags += [ "--prefix", prefix ] if !attributes[:prefix].nil?
+    flags = [ "--root", staging_path ]
+    flags += [ "--prefix", prefix ] if !attributes[:prefix].nil?
+    flags += [ "--ignore-installed" ]
+
     safesystem(*attributes[:python_pip], "install", "--no-deps", *flags, path)
   end # def install_to_staging