* 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

* add a option to force overwrite existing volume

* fix flag

* support called by mount command and /etc/fstab on Linux

* lower case option for system mount is preferred

Close #52

Co-authored-by: NDavies Liu <davies@juicedata.io>