Test bugfix: bugfixed RTOS (mutex, semaphore) - not thread safe stdio causes test result prints to be interrupted by threads' printing

test bugfix: added support for targetID print from device for 'hello world' and 'stdio' testcases
Change "error.h" to "mbed_error.h" to avoid conflicts with 3rd party code
Bumped SDK revision number
Enabled GCC_ARM for NRF51822 targets in official build
Merge branch 'master' of github.com:mbedmicro/mbed