test/py: Update test_bind

As bind-test is now binded at sandbox startup and no more by
test_bind.py, bind-test nodes are not located at the end of
"dm tree" output, but can be located everywhere in the tree, so
bind-test output could either be:

 simple_bus    0  [   ]   generic_simple_bus    |-- bind-test
 phy           0  [   ]   phy_sandbox           |   |-- bind-test-child1
 simple_bus    1  [   ]   generic_simple_bus    |   `-- bind-test-child2

or:

 simple_bus    5  [   ]   generic_simple_bus    `-- bind-test
 phy           2  [   ]   phy_sandbox               |-- bind-test-child1
 simple_bus    6  [   ]   generic_simple_bus        `-- bind-test-child2

in_tree() function need to be updated to take care of that change.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>