Add "mockbin" directory and a fake "su" wrapper for tests

While performing integration tests, the "mockbin" directory is
inserted in the beginning of the $PATH environment variable.

This effectively means that every file placed in this directory will be
executed instead of real one from the system, which opens up the
opportunity to write more complex integration tests.

At the time the only wrapper for "su" command (used in "cmdmod") is
placed there.

tests/integration/__init__.py

@@ -33,6 +33,7 @@ PYEXEC = 'python{0}.{1}'.format(sys.version_info[0], sys.version_info[1])
 
 TMP = os.path.join(INTEGRATION_TEST_DIR, 'tmp')
 FILES = os.path.join(INTEGRATION_TEST_DIR, 'files')
+MOCKBIN = os.path.join(INTEGRATION_TEST_DIR, 'mockbin')
 
 
 def run_tests(TestCase):
@@ -148,6 +149,8 @@ class TestDaemon(object):
                     self.minion_opts['sock_dir'],
                     ],
                    pwd.getpwuid(os.getuid())[0])
+        # Set up PATH to mockbin
+        self._enter_mockbin()
 
         master = salt.master.Master(self.master_opts)
         self.master_process = multiprocessing.Process(target=master.start)
@@ -182,8 +185,25 @@ class TestDaemon(object):
         self.master_process.terminate()
         self.syndic_process.terminate()
         self.smaster_process.terminate()
+        self._exit_mockbin()
         self._clean()
 
+    def _enter_mockbin(self):
+        path = os.environ.get('PATH', '')
+        path_items = path.split(os.pathsep)
+        if MOCKBIN not in path_items:
+            path_items.insert(0, MOCKBIN)
+        os.environ['PATH'] = os.pathsep.join(path_items)
+
+    def _exit_mockbin(self):
+        path = os.environ.get('PATH', '')
+        path_items = path.split(os.pathsep)
+        try:
+            path_items.remove(MOCKBIN)
+        except ValueError:
+            pass
+        os.environ['PATH'] = os.pathsep.join(path_items)
+
     def _clean(self):
         '''
         Clean out the tmp files

tests/integration/mockbin/su

@@ -0,0 +1,12 @@
+#!/bin/bash
+# "Fake" su command
+#
+# Just executes the command without changing effective uid. Used in integration
+# tests.
+while true; do
+    shift
+    test "x$1" == "x-c" && break
+    test "x$1" == "x" && break
+done
+shift
+exec /bin/bash -c "$@"