lib.sh: install func_exit_handler() from start_test()

func_exit_handler() makes sense only when used with start_test()

start_test() is a "mandatory" right now because it's invoked from
lib.sh. But this is wrong because it should be possible to import lib.sh
functions without actually running anything and it's causing various
issues like sof_remove.sh depending on the firmware being loaded, see
discussion in #1169

This commit will make it possible NOT to use start_test().

Signed-off-by: Marc Herbert <marc.herbert@intel.com>

Author: marc-hb

case-lib/hijack.sh

@@ -2,7 +2,6 @@
 
 SUDO_CMD=$(command -v sudo)
 
-trap 'func_exit_handler $?' EXIT
 # Overwrite other functions' exit to perform environment cleanup
 function func_exit_handler()
 {

case-lib/lib.sh

@@ -77,6 +77,9 @@ start_test()
         return 0
     }
 
+    # func_exit_handler() is in hijack.sh
+    trap 'func_exit_handler $?' EXIT
+
     if test -z "$MAX_WAIT_FW_LOADING"; then
         local _pltf; _pltf=$("$SCRIPT_HOME/tools/sof-dump-status.py" -p)
         case "$_pltf" in