Add CLI parsing tests

These test that command lines are parsed to correct Command arguments.
Includes some tests for interactive prompts.

To make this possible cli.run is broken up into several pieces.

ipalib/cli.py

@@ -123,7 +123,7 @@ class textui(backend.Backend):
 
     def __get_encoding(self, stream):
         assert stream in (sys.stdin, sys.stdout)
-        if stream.encoding is None:
+        if getattr(stream, 'encoding', None) is None:
             return 'UTF-8'
         return stream.encoding
 
@@ -1007,7 +1007,11 @@ class cli(backend.Executioner):
     Backend plugin for executing from command line interface.
     """
 
-    def run(self, argv):
+    def get_command(self, argv):
+        """Given CLI arguments, return the Command to use
+
+        On incorrect invocation, prints out a help message and returns None
+        """
         if len(argv) == 0:
             self.Command.help()
             return
@@ -1022,15 +1026,27 @@ class cli(backend.Executioner):
         if name not in self.Command or self.Command[name].NO_CLI:
             raise CommandError(name=key)
         cmd = self.Command[name]
-        if not isinstance(cmd, frontend.Local):
-            self.create_context()
+        return cmd
+
+    def argv_to_keyword_arguments(self, cmd, argv):
+        """Get the keyword arguments for a Command"""
         kw = self.parse(cmd, argv)
         if self.env.interactive:
             self.prompt_interactively(cmd, kw)
         kw = cmd.split_csv(**kw)
         kw['version'] = API_VERSION
         self.load_files(cmd, kw)
+        return kw
+
+    def run(self, argv):
+        cmd = self.get_command(argv)
+        if cmd is None:
+            return
+        name = cmd.name
+        if not isinstance(cmd, frontend.Local):
+            self.create_context()
         try:
+            kw = self.argv_to_keyword_arguments(cmd, argv[1:])
             result = self.execute(name, **kw)
             if callable(cmd.output_for_cli):
                 for param in cmd.params():