Add stub fetch_eggs.py/check_eggs.py for people whose build/test/run

pipelines may have been running these by hand. Print hopefully helpful
information and return 1. Fixes #1030

scripts/check_eggs.py

@@ -0,0 +1 @@
+fetch_eggs.py

scripts/fetch_eggs.py

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+#!/usr/bin/env python
+
+from os import pardir
+from os.path import join, abspath, dirname
+from sys import exit
+
+msg = """
+Eggs in this release of Galaxy have been replaced by Python's newer packaging
+format, wheels. Please use scripts/common_startup.sh to set up your
+environment:
+
+cd {dir} && ./scripts/common_startup.sh
+
+This will create a Python virtualenv and install Galaxy's dependencies into it.
+
+If you start Galaxy using means other than run.sh (as you probably do if you
+are seeing this message), be sure to activate the virtualenv before starting,
+using:
+
+. {venv}/bin/activate
+
+If you already run Galaxy in its own virtualenv, you can reuse your existing
+virtualenv with:
+
+cd {dir} && ./scripts/common_startup.sh --skip-venv
+"""
+
+galaxy = abspath(join(dirname(__file__), pardir))
+venv = join(galaxy, '.venv')
+print msg.format(dir=abspath(join(dirname(__file__), pardir)),
+                 venv=venv)
+exit(1)