Added new command line switches to link with external mbed libraries like: rtos, eth, usb, usb_host, testlib or ublox

This will allow users to link tests against libs. For example it is possible to build network test (like NET_1) using make.py now
Modified make.py so now parameter -n can handle comma separated lists of test names.
Modified make.py so now parameter -n can handle comma separated lists of test names.

Bugfix for option -p