teach mkdir about --exists-okay

adds the --exists-okay flag to the mkdir command, which allows you to
avoid errors if you are calling mkdir to ensure that a directory exists.

ampy/cli.py

@@ -101,8 +101,9 @@ def get(remote_file, local_file):
         local_file.write(contents)
 
 @cli.command()
+@click.option('--exists-okay', is_flag=True)
 @click.argument('directory')
-def mkdir(directory):
+def mkdir(directory, exists_okay):
     """
     Create a directory on the board.
 
@@ -119,7 +120,8 @@ def mkdir(directory):
     """
     # Run the mkdir command.
     board_files = files.Files(_board)
-    board_files.mkdir(directory)
+    board_files.mkdir(directory,
+                      exists_okay=exists_okay)
 
 @cli.command()
 @click.argument('directory', default='/')

ampy/files.py

@@ -105,7 +105,7 @@ def ls(self, directory='/'):
         # Parse the result list and return it.
         return ast.literal_eval(out.decode('utf-8'))
 
-    def mkdir(self, directory):
+    def mkdir(self, directory, exists_okay=False):
         """Create the specified directory.  Note this cannot create a recursive
         hierarchy of directories, instead each one should be created separately.
         """
@@ -123,7 +123,8 @@ def mkdir(self, directory):
         except PyboardError as ex:
             # Check if this is an OSError #17, i.e. directory already exists.
             if ex.args[2].decode('utf-8').find('OSError: [Errno 17] EEXIST') != -1:
-                raise DirectoryExistsError('Directory already exists: {0}'.format(directory))
+                if not exists_okay:
+                    raise DirectoryExistsError('Directory already exists: {0}'.format(directory))
             else:
                 raise ex
         self._pyboard.exit_raw_repl()