boards/z1: fix cc2420_txrx function in CC2420 driver HAL

When waiting for transmission (to CC2420) to be done,
we were wrongly waiting for UCBUSY bit to be set,
while one should actually wait for that bit to be cleared.
tests&examples: use sizeof(stack) in thread_create

fixes #1392
tests&examples: apply coding conventions to sizeof
test: remove superfluous stack size defines
Merge pull request #1388 from rousselk/fix-z1-cc2420-txrx

boards/z1: fix cc2420_txrx function in CC2420 driver HAL
Merge pull request #1393 from LudwigOrtmann/issue-1392

tests/examples cleanup