orch kernutil fix MUSL hang problem due to improper exit (vs _exit)

updated test and doc

docs/README

@@ -17,7 +17,7 @@ The static version limits the allocation to configuration values and does not re
  REQUIREMENTS
 ==============
 
-'orchestrator' runs on GNU/Linux compliant systems with 'BusyBox' (Musl is not completely supported yet). It needs GNU 'make' and a recent compiler (tested on: gcc) for basic features with the following development packages for compilation:
+'orchestrator' runs on GNU/Linux compliant systems also with 'BusyBox', GNU libc, or Musl. It needs GNU 'make' and a recent compiler (tested on: gcc) for basic features with the following development packages for compilation:
 * libnuma-dev		(NUMA manipulation)
 * libcap-dev		(POSIX Capabilities library)
 * check				(CHECK C based run-time test framework)

src/lib/kernutil.c

@@ -582,7 +582,7 @@ popen2(const char * command, const char * type, pid_t * pid)
 		else
 			close(fd[WRITE]);
 
-        exit(EXIT_FAILURE);
+        _exit(EXIT_FAILURE); // use _exit for child process to avoid parent hang!
     }
 
     *pid = child_pid;

test/orchestrator/updateTest.c

@@ -193,11 +193,8 @@ START_TEST(orchestrator_update_stop)
 {	
 	pthread_t thread1;
 	int  iret1;
-#ifdef BUSYBOX
-	int stat1 = 1; // FIXME: MUSL/BUSYBOX start halfway, when dockerlink child process is dead, hangs indefinitely
-#else
 	int stat1 = 0;
-#endif
+
 	iret1 = pthread_create( &thread1, NULL, thread_update, (void*) &stat1);
 	ck_assert_int_eq(iret1, 0);
 
@@ -216,11 +213,8 @@ START_TEST(orchestrator_update_findprocs)
 {	
 	pthread_t thread1;
 	int  iret1;
-#ifdef BUSYBOX
-	int stat1 = 1; // FIXME: MUSL/BUSYBOX start halfway, when dockerlink child process is dead, hangs indefinitely
-#else
 	int stat1 = 0;
-#endif
+
 	pid_t pid1, pid2, pid3;
 	FILE * fd1, * fd2,  * fd3;
 
@@ -274,11 +268,8 @@ START_TEST(orchestrator_update_findprocsall)
 {	
 	pthread_t thread1;
 	int  iret1;
-#ifdef BUSYBOX
-	int stat1 = 1; // FIXME: MUSL/BUSYBOX start halfway, when dockerlink child process is dead, hangs indefinitely
-#else
 	int stat1 = 0;
-#endif
+
 	// set detect mode to pid 
 	free (prgset->cont_pidc);
 	prgset->cont_pidc = strdup(""); // all!
@@ -304,7 +295,7 @@ START_TEST(orchestrator_update_rscs)
 {	
 	pthread_t thread1;
 	int  iret1;
-	int stat1 = 1; // FIXME: MUSL/BUSYBOX start halfway, when dockerlink child process is dead, hangs indefinitely
+	int stat1 = 0;
 	pid_t pid1, pid2;
 	FILE * fd1, * fd2;