Implement legacy XML-RPC interface for ACM commands.

Implement legacy XML-RPC interface for ACM commands.

This patch implements a (non Xen-API) legacy XML-RPC interface for the
ACM commands and funnels the calls into code introduced by the Xen-API
support for ACM security management. Since some of the functionality
has changed, also the xm applications have changed. In particular the
following old commands have been removed along with some tools the
have become obsolete now:

- loadpolicy    (included in: setpolicy)
- makepolicy    (included in: setpolicy)
- cfgbootpolicy (included in: setpolicy)

and the following commands been introduced:

- setpolicy
- getpolicy
- resetpolicy

All tools have been adapted to work in Xen-API and legacy XML-RPC
mode. Both modes support the same functionality.

Signed-off-by: Stefan Berger <stefanb@us.ibm.com>