btaddon scripts: warn for pyserial

tools/btaddon/hc06_console_AT.py

@@ -2,7 +2,11 @@
 
 import sys
 import time
-import serial
+try:
+    import serial
+except ModuleNotFoundError:
+    print("Please install pyserial module first.")
+    sys.exit(1)
 
 if len(sys.argv) < 2:
     print('Usage: %s <baudrate>' % sys.argv[0])

tools/btaddon/hc06_factory.py

@@ -1,7 +1,13 @@
 #!/usr/bin/env python3
 
 import time
-import serial
+import sys
+
+try:
+    import serial
+except ModuleNotFoundError:
+    print("Please install pyserial module first.")
+    sys.exit(1)
 
 name = b'PM3_RDV4.0'
 pin  = b'1234'