Use ceph-fuse to mount CephFS

The upstream documentation:

* nautilus - https://docs.ceph.com/docs/nautilus/cephfs/fuse/
* master - https://docs.ceph.com/docs/master/cephfs/fuse/

Steps to assert ceph-fuse is working

First, deploy a cluster with at least one MDS running.

Second, decide if you will run ceph-fuse as root or as a normal user and decide which machine will be the "client machine" (it must not be a part of the Ceph cluster).

Third, on the client machine, install /etc/ceph/ceph.conf and /etc/ceph/ceph.client.admin.keyring by copying these files from a MON node. If using non-root user, make sure both files have permissions 644 and the containing directory has permissions 755.

Fourth, on the client machine, install the ceph-fuse package.

Fifth, if using a normal user, make sure that user exists on the client machine and is a member of the ceph group.

Sixth, if using a normal user, set 'user_allow_other' in /etc/fuse.conf.

Seventh, get the IP address of a MON node by looking inside /etc/ceph.conf:

$ grep mon_host /etc/ceph/ceph.conf
mon_host = 10.20.24.200

Eighth, create a mount point:

$ mkdir ~/cephfs
$ ls ~/cephfs
$

Ninth, mount cephfs using the IP address of the MON found in step 6:

$ ceph-fuse -m 10.20.24.200 ~/cephfs
2019-11-29 13:51:13.688 7fafe9757040 -1 init, newargv = 0x5581396d32c0 newargc=7
ceph-fuse[27795]: starting ceph client
ceph-fuse[27795]: starting fuse
$

Tenth, when done, unmount cephfs:

$ fusermount -u ~/cephfs