librados option 'conf' and 'cluster'.

[Javen Wu <javen.wu@xtaotech.com>]

Hi buddies,

Recently, I met a problem about librados option 'conf' and 'cluster'.
I created a CEPH cluster but not name it 'ceph', it triggers a lot of 
problems
on my openstack environment.
I found there are consumers of librados or librados python binding only 
respect
  'conf' option. However, the option 'cluster' is ignored usually.

So far, I suffered the problem in:
1. librados python binding
2. qemu rbd driver
3. cinder volume rbd driver

I saw there is rados_create2() API in librados besides rados_create(), but
it seems the API is not widedly used by consumers yet.

I am thinking whether we can do a compromise in librados. If consumers of
librados does not give an arguments for 'cluster'(cluster name) explicitly,
Can we use (basename(conffile).split('.conf')[0]) as cluster name by
default in librados?

So that all consumers of the librados can tolerate the non-'ceph' 
cluster name
without any change.

How do you guys think? If you agree to the change, I can do the quick 
fixing.

Thanks
Javen