* Lookup with lua script to save redis calls

* Use EvalSHA to avoid sending the script repeatedly

* Address comments

* Refactor, make buildSlice a function instead

* Make parseSlice a function

* Refactor, extract a function

* Refactor to make it easier to benchmark

* More fine-grained benchmarks

* Make slices parsing faster by pre-allocating slices

* renamed method receiver to be consistent

* golint messages for logger, buffer, alloc..

* compress and cond golint fix

* review changes

This reverts commit e56e2d86.

symlink can't be changed, so it's safe to cache

* wait for mount point to be ready

* update tests

* delete all chunks together

* update comment

* cleanup

* fix lint error

* fix rename

Some of redis may lack some field, it shows confusing warning:

```
2021/01/16 10:13:39.691143 juicefs[11836] <WARNING>: parse info: parseRedisInfo: not all fields found
2021/01/16 10:13:39.691170 juicefs[11836] <INFO>: Checking Redis server configuration
2021/01/16 10:13:39.691196 juicefs[11836] <WARNING>: AOF is not enabled, you may lose data if Redis is not shutdown properly.
2021/01/16 10:13:39.691213 juicefs[11836] <WARNING>: maxmemory_policy is "volatile-lru", please set it to 'noeviction'.
```

After this, it will show:

```
2021/01/16 10:13:39.691213 juicefs[11836] <WARNING>: maxmemory_policy is "volatile-lru", please set it to 'noeviction'.
```

* change to use lower case for command line options

* cleanup options

* Check Redis Server configuration

* Complete the test

* Remove unwanted change

* Log specific warnning messages for each kind of violation

* Use librados to access Ceph

* build juicefs with librados

* add ceph as dep

* Optimized logging level by default only logging to syslog in daemon mode

* Fix review comments

* delete xattr data when removing files

* delete xattr data when removing direcotry