Fix for issue with libraries being built out of order

[bridadan]

I introduced a regression a while ago that builds library dependencies out of order when building tests. This PR fixes that regression.

Library dependencies are now built in the order they are specified in the test's definition in tests.py.

Ex. for the test NET_1, its definition looks like this in tests.py:

    {
        "id": "NET_1", "description": "TCP client hello world",
        "source_dir": join(TEST_DIR, "net", "helloworld", "tcpclient"),
        "dependencies": [MBED_LIBRARIES, RTOS_LIBRARIES, ETH_LIBRARY, TEST_MBED_LIB],
        "duration": 15,
        "automated": True,
        "peripherals": ["ethernet"],
    },

You can see the order in which the library dependencies will be built by examining the dependencies key.

[0xc0170]

Can you share which PR which changed this previously?

[0xc0170]

Found it #1040 :-)