Add SSH Agent Primitives and usage

Debugging some issues revealed a problem in the __eq__ method that is
patched here. This produced some red herring backtraces unnecessarily.

It's worth noting that close_fds on this subprocess.Popen call is
critical to the health of any other processes being spawned from Zuul.
Without it, git processes run by the git module went defunct and locked
things up in weird ways.

Change-Id: I6875568f4b7ccf261491c45086727250e58f5ed8
diff --git a/tests/base.py b/tests/base.py
index 0f8b3af..4dd4c64 100755
--- a/tests/base.py
+++ b/tests/base.py
@@ -1837,12 +1837,20 @@
 
         # Make per test copy of Configuration.
         self.setup_config()
+        self.private_key_file = os.path.join(self.test_root, 'test_id_rsa')
+        if not os.path.exists(self.private_key_file):
+            src_private_key_file = os.path.join(FIXTURE_DIR, 'test_id_rsa')
+            shutil.copy(src_private_key_file, self.private_key_file)
+            shutil.copy('{}.pub'.format(src_private_key_file),
+                        '{}.pub'.format(self.private_key_file))
+            os.chmod(self.private_key_file, 0o0600)
         self.config.set('zuul', 'tenant_config',
                         os.path.join(FIXTURE_DIR,
                                      self.config.get('zuul', 'tenant_config')))
         self.config.set('merger', 'git_dir', self.merger_src_root)
         self.config.set('executor', 'git_dir', self.executor_src_root)
         self.config.set('zuul', 'state_dir', self.state_root)
+        self.config.set('executor', 'private_key_file', self.private_key_file)
 
         self.statsd = FakeStatsd()
         # note, use 127.0.0.1 rather than localhost to avoid getting ipv6