bug: repeated execution of `make run` will start multiple nginx processes, while `make stop` can only stop one

[kevhoo]

Issue description

重复执行 make run 会启动多个master进程，而 make stop 只能停止一个

Environment

• apisix version (cmd: apisix version): 1.3
• OS: centos7

Minimal test code / Steps to reproduce the issue

1. cd apisix/
2. make run
3. make run
4. ps aux | grep apisix | grep master

What's the actual result? (including assertion message & call stack if applicable)

系统启动了两个 openresty 实例

What's the expected result?

如果已有运行中的openresty实例，则不需要再启动新的实例

思路：判断/logs/nginx.pid 存在，表示服务已启动

Makefile line 82 ~ 84
        mkdir -p logs
        mkdir -p /tmp/apisix_cores/
        $(OR_EXEC) -p $$PWD/ -c $$PWD/conf/nginx.conf

修改为：

ifeq ("$(wildcard logs/nginx.pid)", "")
	mkdir -p logs
	mkdir -p /tmp/apisix_cores/
	$(OR_EXEC) -p $$PWD/ -c $$PWD/conf/nginx.conf
else
	@echo "Apisix is running..."
endif

[membphis]

welcome PR

[membphis]

We can add this check logic in CLI(bin/apisix).

[jie123108]

I want to fix it