daemon: Fix segfault when USE_SMACK is disabled

If USE_SMACK is not enabled, the smack label value is never set or
allocated, resulting in a segfault when attempting to free it.

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>
libbuxton: Correctly handle priorities

Previously we attempted to check if priority was less than a new
layer priority.
This commit resolves the issue by checking whether the priority is
less than or equal to 0, so that base is included in priority checking.

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>
daemon: Track changes in key values

We'll now track the changes in values for clients, tracking the old
value they first had upon registration and subsequent set's. The
client will now recieve both the old and new values when they're
informed of the change.

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>
Track UID in BuxtonClient

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>
Make user layers work correctly

Simply put we use the connecting clients uid in order to separate
user layers.

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>
db: Use unique internal names

We need to fully separate user databases, which means uniquely naming
them in the backends. If the name separation is not done, we could
return the wrong database for each client.

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>
Minor documentation fixes (Doxygen errors)

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>
shared: old_data is already a pointer so just pass it

Signed-off-by: William Douglas <william.douglas@intel.com>
db: Free allocated db name

Signed-off-by: William Douglas <william.douglas@intel.com>