add pkg-map to pip-and-virtualenv element

Add a pkg-map file so that Gentoo can avoid polluting the FS with
files not tracked in the package manager.

Changed the directory name so that the source-install method would
actually be disabled when DIB_INSTALLTYPE_pip_and_virtualenv=package
is set.  Also changed source-repository line to be consistent with
the element name.

Change-Id: I5225bd7113ff2588c755ad4cd4ae9a2d78fff196

elements/pip-and-virtualenv/pkg-map

@@ -0,0 +1,8 @@
+{
+  "family": {
+    "gentoo": {
+      "python-pip": "dev-python/pip",
+      "python-virtualenv": "dev-python/virtualenv"
+    }
+  }
+}

elements/pip-and-virtualenv/source-repository-pip-and-virtualenv

@@ -1 +1 @@
-get-pip-py file /tmp/get-pip.py https://bootstrap.pypa.io/get-pip.py
+pip-and-virtualenv file /tmp/get-pip.py https://bootstrap.pypa.io/get-pip.py