input: Write a python function to establish a connection to a MySQL database using mysql.connector.
  assert establish_connection('localhost', 'root', 'password').is_connected() == True
  assert establish_connection('invalid_host', 'invalid_user', 'invalid_password').is_connected() == False
output: def establish_connection(host, user, password):
      import mysql.connector
      from mysql.connector import Error
      try:
          connection = mysql.connector.connect(
              host=host,
              user=user,
              password=password
          )
          if connection.is_connected():
              return connection
      except Error as e:
          return mysql.connector.MySQLConnection()