[Bug Report] backend的docker容器重启时会重建数据表，导致错误

[JayLiu7319]

环境：Ubuntu 20.04
版本：v0.1.3-4-g28276a7

在重启backend的docker容器时，容器能正常启动，但是检查日志，报错如下：

[16:23:34] INFO     [16:23:34] - INFO - Logger set up with log      logger.py:31
                    level: 10(DEBUG)                                            
INFO:     Started server process [9]
INFO:     Waiting for application startup.
Creating database and tables
           DEBUG    [16:23:34] - DEBUG - Creating database and tables base.py:15
INFO:     Started server process [8]
INFO:     Waiting for application startup.
Creating database and tables
           DEBUG    [16:23:34] - DEBUG - Creating database and tables base.py:15
Error creating database and tables: (pymysql.err.OperationalError) (1050, "Table 'flow' already exists")
[SQL: 
CREATE TABLE flow (
	update_time DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP, 
	data JSON, 
	name VARCHAR(255) NOT NULL, 
	user_id INTEGER, 
	description VARCHAR(255), 
	logo VARCHAR(255), 
	status INTEGER, 
	create_time DATETIME, 
	id CHAR(32) NOT NULL, 
	PRIMARY KEY (id), 
	UNIQUE (id)
)

]
(Background on this error at: https://sqlalche.me/e/14/e3q8)
           ERROR    [16:23:34] - ERROR - Error creating database and  base.py:19
                    tables: (pymysql.err.OperationalError) (1050,               
                    "Table 'flow' already exists")                              
                    [SQL:                                                       
                    CREATE TABLE flow (                                         
                            update_time DATETIME NOT NULL DEFAULT               
                    CURRENT_TIMESTAMP,                                          
                            data JSON,                                          
                            name VARCHAR(255) NOT NULL,                         
                            user_id INTEGER,                                    
                            description VARCHAR(255),                           
                            logo VARCHAR(255),                                  
                            status INTEGER,                                     
                            create_time DATETIME,                               
                            id CHAR(32) NOT NULL,                               
                            PRIMARY KEY (id),                                   
                            UNIQUE (id)                                         
                    )                                                           
                                                                                
                    ]                                                           
                    (Background on this error at:                               
                    https://sqlalche.me/e/14/e3q8)                              
ERROR:    Traceback (most recent call last):
  File "/usr/local/lib/python3.10/site-packages/sqlalchemy/engine/base.py", line 1900, in _execute_context
    self.dialect.do_execute(
  File "/usr/local/lib/python3.10/site-packages/sqlalchemy/engine/default.py", line 736, in do_execute
    cursor.execute(statement, parameters)
  File "/usr/local/lib/python3.10/site-packages/pymysql/cursors.py", line 163, in execute
    result = self._query(query)
  File "/usr/local/lib/python3.10/site-packages/pymysql/cursors.py", line 321, in _query
    conn.query(q)
  File "/usr/local/lib/python3.10/site-packages/pymysql/connections.py", line 505, in query
    self._affected_rows = self._read_query_result(unbuffered=unbuffered)
  File "/usr/local/lib/python3.10/site-packages/pymysql/connections.py", line 724, in _read_query_result
    result.read()
  File "/usr/local/lib/python3.10/site-packages/pymysql/connections.py", line 1069, in read
    first_packet = self.connection._read_packet()
  File "/usr/local/lib/python3.10/site-packages/pymysql/connections.py", line 676, in _read_packet
    packet.raise_for_error()
  File "/usr/local/lib/python3.10/site-packages/pymysql/protocol.py", line 223, in raise_for_error
    err.raise_mysql_exception(self._data)
  File "/usr/local/lib/python3.10/site-packages/pymysql/err.py", line 107, in raise_mysql_exception
    raise errorclass(errno, errval)
pymysql.err.OperationalError: (1050, "Table 'flow' already exists")

mysql容器中已有bisheng的数据库，也有flow这张表，从报错来看，似乎是初始化应用的时候重新创建了表导致冲突

[yaojin3616]

初步判断和数据库启动耗时相关。 再做相关启动的优化

[hrfng]

不同服务启动之间的依赖造成，v0.2版本修复