cephfs provisioner leaks Secret objects

[farcaller]

The cephfs provisioner doesn't clean up Secret objects (doesn't re-use them either), and doesn't clean up the actual users from ceph, leaving them dangling with some permissions:

client.kubernetes-dynamic-user-8e229ae4-c4a5-11e7-ad64-0adc8221b842
	key: 
	caps: [mds] allow r
	caps: [mon] allow r
	caps: [osd]

Instead the provisioner should return the storage to the same state it was before the PVC was created.

[wongma7]

/assign @rootfs
kind of related, we should no longer be creating secrets in same namespace as pvc anyhow: #309

[rootfs]

the provisioner deauthorize the user when deleting the share.

Maybe the cap is not all that is expected in the library here, since mds is given allow r here to work around a kernel cephfs issue.

[rootfs]

@cofyc do you have a chance to look into this? thanks

[cofyc]

@rootfs
OK, I will take a look at it.

[JrCs]

My PR #466 only remove ceph user if it's name start with kubernetes-dynamic-user-