Implement a set of python bindings for the sysdb with feature set
similar to what is available in the tools. The primary
consumers would be applications like system-config-users.

Resolves: Ticket #102

The configuration options krb5ccache_dir and krb5ccname_template
are added to the Kerberos provider to create the user's credential
caches the same way as pam_krb5 does. Due to the design of the sssd
and the supported ccache types of MIT Kerberos only files are
allowed.

The code was still dependent on it for the ldap driver.
Changed the driver code to depend on the schema type.
Fix defaults for user and groups trees.
ATM if you use the rfc2307bis schema you have to put users and groups
in 2 separate trees (what people does by default anyway.
If this limitation will turn to be too hard, we will change this later.

Because the confdb always operates synchronously, it maintains its
own private event context internally. The event context argument
passed to it is never used, so we'll remove it to avoid confusion.

The special persistent local database retains the original name.
All other backends now have their own cache-NAME.ldb file.

Also add tests