Fix couple of nit picks

Fixed two nit picks:

1) in service_instance module was improper statement about amount of
external methods.

2) After commit merge
https://github.com/openstack/manila/commit/883e02f2

part of etc/manila/README.manila.conf info became outdated.

Change-Id: I68b9efc9bc1f701cb4ea8dbecf69ec58f7cb5df3
Merge "Fix couple of nit picks"