tinfoil: pass datastore to server when expanding python references

tinfoil: pass datastore to server when expanding python references

If you're expanding a value that refers to the value of a variable in
python code, we need to ensure that the datastore that gets used to get
the value of that variable is the client-side datastore and not just the
part of it that's on the server side. For example, suppose you are in
client code doing the following:

d.setVar('HELLO', 'there')
result = d.expand('${@d.getVar("HELLO", True)}')

result should be "there" but if the client part wasn't taken into
account, it would be whatever value HELLO had in the server portion of
the datastore (if any).

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>