Raise key length defaults

Extend RSA keylength to 2048 bits by default,
as the previous default of 1024 bit is considered
weak since 12/31/2010.

Also unify the message_md to the openssl builtin
default.

Fixes bug 1103002

Change-Id: I619fc32b62beab4458ee6f21bf8dc7499fe400d7
Merge " Cleanup docstrings " from keystone/common/cms.py

In an attempt to unify both implementations in order to
be able to remove one of the duplicated ones, merge the
changes from this commit in keystone:

    Author: Dolph Mathews <dolph.mathews@gmail.com>
    Date:   Fri May 24 11:36:44 2013 -0500

    Cleanup docstrings (flake8 H401, H402, H403, H404)

Change-Id: Ib23c9ab5066cfdcdda4e07cd30fa8f6ff47949bd
Merge "Merge " Cleanup docstrings " from keystone/common/cms.py"
Merge "Raise key length defaults"