tests: use _ instead of - in environment variables

Contrary to bash, dash filters out environment variables containing
'-' characters. And for example, /bin/sh is dash on Debian.

Rebase instructions:
- squash with 93369b04
  and keep the above commit message

fixup! Fix testing index when /bin/sh is dash (like on Debian)

bootstrap/bootstrap.py

@@ -139,7 +139,7 @@ cmd = [sys.executable, '-c',
        '-mZqNxd', tmpeggs]
 
 find_links = os.environ.get(
-    'bootstrap-testing-find-links',
+    'bootstrap_testing_find_links',
     options.find_links or
     ('http://downloads.buildout.org/'
      if options.accept_buildout_test_releases else None)

src/zc/buildout/tests.py

@@ -3394,8 +3394,8 @@ extdemo_setup_py = r"""
 import os, sys
 from distutils.core import setup, Extension
 
-if os.environ.get('test-variable'):
-    print("Have environment test-variable: %%s" %% os.environ['test-variable'])
+if os.environ.get('test_variable'):
+    print("Have environment test_variable: %%s" %% os.environ['test_variable'])
 
 setup(name = "extdemo", version = "%s", url="http://www.zope.org",
       author="Demo", author_email="demo@demo.com",
@@ -3539,7 +3539,7 @@ def bootstrapSetup(test):
     ws = getWorkingSetWithBuildoutEgg(test)
     makeNewRelease('zc.buildout', ws, sample_eggs, '2.0.0')
     makeNewRelease('zc.buildout', ws, sample_eggs, '22.0.0')
-    os.environ['bootstrap-testing-find-links'] = test.globs['link_server']
+    os.environ['bootstrap_testing_find_links'] = test.globs['link_server']
     test.globs['bootstrap_py'] = bootstrap_py
 
 normalize_bang = (

zc.recipe.egg_/src/zc/recipe/egg/custom.rst

@@ -246,7 +246,7 @@ We won't get an update.
     -  zc.recipe.egg.egg-link
 
 But if we run the buildout in the default on-line and newest modes, we
-will. This time we also get the test-variable message again, because the new
+will. This time we also get the test_variable message again, because the new
 version is imported:
 
     >>> print_(system(buildout), end='') # doctest: +ELLIPSIS
@@ -318,8 +318,8 @@ recipe was run.
     ...
     ...     def install(self):
     ...         logging.getLogger(self.name).info(
-    ...             'test-variable left over: %s' % (
-    ...                 'test-variable' in os.environ))
+    ...             'test_variable left over: %s' % (
+    ...                 'test_variable' in os.environ))
     ...         return []
     ...
     ...     def update(self):
@@ -345,7 +345,7 @@ Create our buildout:
     ... parts = extdemo checkenv
     ...
     ... [extdemo-env]
-    ... test-variable = foo
+    ... test_variable = foo
     ...
     ... [extdemo]
     ... recipe = zc.recipe.egg:custom
@@ -363,13 +363,13 @@ Create our buildout:
     Uninstalling demo.
     Uninstalling extdemo.
     Installing extdemo.
-    Have environment test-variable: foo
+    Have environment test_variable: foo
     zip_safe flag not set; analyzing archive contents...
     Installing checkenv.
     ...
 
 
-The setup.py also printed out that we have set the environment `test-variable`
+The setup.py also printed out that we have set the environment `test_variable`
 to foo. After the buildout the variable is reset to its original value (i.e.
 removed).
 
@@ -377,14 +377,14 @@ When an environment variable has a value before zc.recipe.egg:custom is run,
 the original value will be restored:
 
     >>> import os
-    >>> os.environ['test-variable'] = 'bar'
+    >>> os.environ['test_variable'] = 'bar'
     >>> print_(system(buildout), end='')
     Develop: '/sample-buildout/recipes'
     Updating extdemo.
     Updating checkenv.
-    checkenv: test-variable left over: True
+    checkenv: test_variable left over: True
 
-    >>> os.environ['test-variable']
+    >>> os.environ['test_variable']
     'bar'
 
 
@@ -399,7 +399,7 @@ are interpolated with os.environ before the're set:
     ... parts = extdemo checkenv
     ...
     ... [extdemo-env]
-    ... test-variable = foo:%%(test-variable)s
+    ... test_variable = foo:%%(test_variable)s
     ...
     ... [extdemo]
     ... recipe = zc.recipe.egg:custom
@@ -416,14 +416,14 @@ are interpolated with os.environ before the're set:
     Develop: '/sample-buildout/recipes'
     Uninstalling extdemo.
     Installing extdemo.
-    Have environment test-variable: foo:bar
+    Have environment test_variable: foo:bar
     zip_safe flag not set; analyzing archive contents...
     Updating checkenv.
     ...
 
-    >>> os.environ['test-variable']
+    >>> os.environ['test_variable']
     'bar'
-    >>> del os.environ['test-variable']
+    >>> del os.environ['test_variable']
 
 
 Create a clean buildout.cfg w/o the checkenv recipe, and delete the recipe: