This commit adds the test developed by Jan Staschulat with Issue #incubator_nuttx/2935
It is expected to cause the OS test to fail for the time being since that issue reports a bug.
Tested using the (new) stm32f4discovery:sporadic configuratioin.
include/ and netutils/: Remove references to CONFIG_DISABLE_SIGNALS. Signals can no longer be disabled.
nshlib/: Remove references to CONFIG_DISABLE_SIGNALS. Signals can no longer be disabled.
system/: Remove references to CONFIG_DISABLE_SIGNALS. Signals can no longer be disabled.
testing/: Remove references to CONFIG_DISABLE_SIGNALS. Signals can no longer be disabled.
examples/: Remove references to CONFIG_DISABLE_SIGNALS. Signals can no longer be disabled.