All the core examples have been modified not to return from main
by the means of the return statement, but rather via exit() function,
which was done to make the examples more bare metal friendly.
This commit, for the sake of consistency, introduces the modifications
to the test and utility examples. These, while less likely to be used
in the low level environments, won't suffer from such a change.
The idea is to use the simple program that is expected to be modified
rarely to set a breakpoint in a specific line and check that the
function mbedtls_zeroize() does actually set the buffer to 0 and is not
optimised out by the compiler.
