Linux CommandExecutor

The CommandExecutor helper class can execute shell commands in blocking and non-blocking mode
This class is able to execute processes by using the Linux popen call. It also has the capability of writing
the read output of a process into a provided ring buffer.

The executor works by first loading the command which should be executed and specifying whether
it should be executed blocking or non-blocking. After that, execution can be started with the execute call.

Using non-blocking mode allows to execute commands which might take a longer time in the background,
and allowing the user thread to check completion status with the check function

Moved to HAL like requested in code review and unit tested with failing commands as well.
Also, Linux HAL components are compiled by default now unless explicitely disabled.

@@ -0,0 +72,4 @@
+        result = cmdExecutor.check(bytesHaveBeenRead);
+        REQUIRE(result != CommandExecutor::COMMAND_ERROR);
+        usleep(500);
+        REQUIRE(limitIdx < 20);