Wrong file name used when log file exists checking

[CarpenterLee]

Issue Description

Type: bug report

Describe what happened (or what feature you want)

DateFileLogHandler.logFileExits() method uses a wrong log file name when checking log file exists, this will lead trying to recreate the log file at every log writing, which will cause performance problem.

Describe what you expected to happen

Use the right log file name when exists checking.

How to reproduce it (as minimally and precisely as possible)

1. Invoke RecordLog.info() in high concurrency;
2. Use jstack pid to see the stack trace of the current process, then we will see many threads BLOCKED at com.alibaba.csp.sentinel.log.DateFileLogHandler.publish().

Tell us your environment

None.

Anything else we need to know?

None.