builder: include environment when running an exec

Some container execs have an environment, let's make sure they are
included when running exec.

Closes-Bug: #1855932
Change-Id: Ic2e2c2d50f5883f7db28768ba215e74bcbf9fd8b
(cherry picked from commit b5be45067a)

paunch/builder/base.py

@@ -266,6 +266,7 @@ class BaseBuilder(object):
             cmd.append('--privileged=%s' % str(cconfig['privileged']).lower())
         if 'user' in cconfig:
             cmd.append('--user=%s' % cconfig['user'])
+        self.list_or_dict_arg(cconfig, cmd, 'environment', '--env')
         command = self.command_argument(cconfig.get('command'))
         # for exec, the first argument is the container name,
         # make sure the correct one is used

paunch/tests/test_builder_base.py

@@ -583,6 +583,7 @@ three-12345678 three''', '', 0),
             'one': {
                 'command': 'ls -l /foo',
                 'privileged': True,
+                'environment': {'FOO': 'BAR'},
                 'user': 'bar'
             }
         }
@@ -594,6 +595,7 @@ three-12345678 three''', '', 0),
         self.assertEqual(
             ['docker', 'exec',
              '--privileged=true', '--user=bar',
+             '--env=FOO=BAR',
              'one-12345678', '-l', '/foo'],
             cmd
         )