sanitycheck failed issue in parallel running.

[chen-png]

Describe the bug
use the sanitycheck to run all tests with four boards, it failed with error "generated an exception: [Errno 24] Too many open files", i found this error is caused by the code "log_out_fp = open(self.log, "wt")" in DeviceHandler, the system limits the max open files to 1024.
then I modified the /etc/secruity/limits.conf to set the limited open files to 2048, and run sanitycheck again, it failed with "ValueError: filedescriptor out of range in select()", caused by code" readable, _, _ = select.select(readlist, [], [], self.timeout)

To Reproduce
Steps to reproduce the behavior:

1. connect four boars to pc and run all tests use sanitycheck
2. sanitycheck --generate-hardware-map map4.yml
3. sanitycheck --hardware-map map4.yml --device-testing -T tests -v
4. See error

Screenshots or console output

Exception in thread Thread-635:
Traceback (most recent call last):
File "/usr/lib64/python3.6/threading.py", line 916, in _bootstrap_inner
self.run()
File "/usr/lib64/python3.6/threading.py", line 864, in run
self._target(*self._args, **self._kwargs)
File "/home/chenpeng/zephyrproject/zephyr/scripts/sanitycheck", line 628, in monitor_serial
readable, _, _ = select.select(readlist, [], [], self.timeout)
ValueError: filedescriptor out of range in select()

INFO - 666/720 mimxrt1050_evk tests/arch/arm/arm_interrupt/arch.interrupt.no_optimizations FAILED N/A (device 8.871s)
ERROR - see: sanity-out/mimxrt1050_evk/tests/arch/arm/arm_interrupt/arch.interrupt.no_optimizations/build.log
Exception in thread Thread-636:
Traceback (most recent call last):
File "/usr/lib64/python3.6/threading.py", line 916, in _bootstrap_inner
self.run()
File "/usr/lib64/python3.6/threading.py", line 864, in run
self._target(*self._args, **self._kwargs)
File "/home/chenpeng/zephyrproject/zephyr/scripts/sanitycheck", line 628, in monitor_serial
readable, _, _ = select.select(readlist, [], [], self.timeout)
ValueError: filedescriptor out of range in select()

Environment (please complete the following information):

• OS: fedora28
• Toolchain: zephyr-sdk-0.10.3
• Commit ID: 4e135d7

[aescolar]

CC @nashif

[nashif]

duplicate of #20974