Fix Issue #102

[yatch]

This PR introduces two changes for Issue #102:

• create a separate firmware file for each mote (applied only to --testbed=opentestbed case)
• reset a mote before programming

When programming motes one by one with a certain interval, cc2538-bsl.py fails saying "Timeout waiting for ACK/NACK after 'Synch (0x55 0x55)'". I suspected that the serial port was not cleanly released when cc2538-bsl.py started, but seems this is not true.

After some trial-and-error iterations, I found resetting a mote just before programming gives better success rate for programming.

Here are logs of my script after adding reset() to `_mqtt_handler_program():

2019-06-03 16:41:11,516: [INFO] Start programming "openwsn-openmote-b-24ghz.ihex" to 00-12-4b-00-14-b5-b5-77
2019-06-03 16:41:14,521: [INFO] Start programming "openwsn-openmote-b-24ghz.ihex" to 00-12-4b-00-14-b5-b5-9b
2019-06-03 16:41:17,524: [INFO] Start programming "openwsn-openmote-b-24ghz.ihex" to 00-12-4b-00-14-b5-b6-06
2019-06-03 16:41:20,529: [INFO] Start programming "openwsn-openmote-b-24ghz.ihex" to 00-12-4b-00-14-b5-b6-30
2019-06-03 16:41:24,693: [INFO] Succeed to program "openwsn-openmote-b-24ghz.ihex" to 00-12-4b-00-14-b5-b5-77
2019-06-03 16:41:27,523: [INFO] Succeed to program "openwsn-openmote-b-24ghz.ihex" to 00-12-4b-00-14-b5-b5-9b
2019-06-03 16:41:30,670: [INFO] Succeed to program "openwsn-openmote-b-24ghz.ihex" to 00-12-4b-00-14-b5-b6-06
2019-06-03 16:41:33,290: [INFO] Succeed to program "openwsn-openmote-b-24ghz.ihex" to 00-12-4b-00-14-b5-b6-30

Without reset(), programing failed 3 out of 4:

2019-06-03 16:36:54,014: [INFO] Start programming "openwsn-openmote-b-24ghz.ihex" to 00-12-4b-00-14-b5-b5-77
2019-06-03 16:36:57,018: [INFO] Start programming "openwsn-openmote-b-24ghz.ihex" to 00-12-4b-00-14-b5-b5-9b
2019-06-03 16:37:00,021: [INFO] Start programming "openwsn-openmote-b-24ghz.ihex" to 00-12-4b-00-14-b5-b6-06
2019-06-03 16:37:03,026: [INFO] Start programming "openwsn-openmote-b-24ghz.ihex" to 00-12-4b-00-14-b5-b6-30
2019-06-03 16:37:03,099: [ERROR] Failed to program "openwsn-openmote-b-24ghz.ihex" to 00-12-4b-00-14-b5-b5-9b
2019-06-03 16:37:06,010: [ERROR] Failed to program "openwsn-openmote-b-24ghz.ihex" to 00-12-4b-00-14-b5-b6-06
2019-06-03 16:37:09,045: [INFO] Succeed to program "openwsn-openmote-b-24ghz.ihex" to 00-12-4b-00-14-b5-b5-77
2019-06-03 16:37:09,072: [ERROR] Failed to program "openwsn-openmote-b-24ghz.ihex" to 00-12-4b-00-14-b5-b6-30

This PR has other minor improvements as well.

[yatch]

Fix Issue #104 as well.

[yatch]

discovermotes sometimes fails with the same error, "Timeout waiting for ACK/NACK after 'Synch (0x55 0x55)"

Traceback (most recent call last):
  File "/home/opentestbed/latest/otbox.py", line 380, in _execute_command_safely
    returnVal['returnVal'] =  cmd_handler(deviceType, deviceId, payload)
  File "/home/opentestbed/latest/otbox.py", line 471, in _mqtt_handler_discovermotes
    firmware_file         = self.tb.firmware_eui64_retrieval,
  File "/home/opentestbed/latest/otbox.py", line 699, in _bootload_motes
    raise RuntimeError(stdout, stderr)
RuntimeError: ('', "Opening port /dev/openmote-b_3, baud 400000\nReading data from /home/opentestbed/latest/bootloaders/opentestbed/01bsp_eui64_prog.ihex\nYour firmware looks like an Intel Hex file\nConnecting to target...\nERROR: Timeout waiting for ACK/NACK after 'Synch (0x55 0x55)'\n")