Per discussion with the desktop team, using the org.freedesktop
interface name will simplify adoption, as potential users won't
feel like they're pulling in a FreeIPA dependency.

Also shorten names oh other user attributes.

Also unify SYSDB_PW_NAME and SYSDB_GR_NAME in SYSDB_NAME and make it "name"

Calulates next id automatically if uid/gid are not specified.
Fixes to sysdb_get_next_available_id.
Add tests to create users and groups through the new functions.

SetUserAttributes is now available for use in the Infopipe.
I also reorganized a few of the internal InfoPipe objects to
reduce code duplication.

One very simple test is included in this checkin to validate that
the parser is working.

This patch adds support for requesting user data in the sysdb via
the InfoPipe. It currently has support for reading defined entries
of integral, floating-point or string types.

Tasks remaining:
1) Implement call to the provider when cache is out of date
2) Support byte arrays for userpic and similar

I modified sysdb_search_ctx in sysdb_search.c to accept an array of
attributes to pass into the LDB search.

I also made one additional related fix: the btreemap now sorts in the
correct order. Previously I had accidentally transposed the two
values for sorting, so the map would always have been in exact
reverse order.