Werk #4755: Fixed possible error when processing piggyback monitoring data

An error "OSError: [Errno 2] No such file or directory: '/omd/sites/*/tmp/check_mk/piggyback/'" could occur when using piggyback agent data (like it's done when monitoring ESX hosts / vcenters).

The error message was visible in the cmc.log and looked like this:

2017-06-06 06:39:36 [4] Check_MK helper [7231]: : >> File "/omd/sites/mysite/share/check_mk/modules/check_mk_base.py", line 371, in get_host_info 2017-06-06 06:39:36 [4] Check_MK helper [7231]: : >> ignore_check_interval=True) 2017-06-06 06:39:36 [4] Check_MK helper [7231]: : >> File "/omd/sites/mysite/share/check_mk/modules/check_mk_base.py", line 506, in get_realhost_info 2017-06-06 06:39:36 [4] Check_MK helper [7231]: : >> piggy_output = get_piggyback_info(hostname) + get_piggyback_info(ipaddress) 2017-06-06 06:39:36 [4] Check_MK helper [7231]: : >> File "/omd/sites/mysite/share/check_mk/modules/check_mk_base.py", line 635, in get_piggyback_info 2017-06-06 06:39:36 [4] Check_MK helper [7231]: : >> for sourcehost, file_path in get_piggyback_files(hostname): 2017-06-06 06:39:36 [4] Check_MK helper [7231]: : >> File "/omd/sites/mysite/share/check_mk/modules/check_mk_base.py", line 612, in get_piggyback_files 2017-06-06 06:39:36 [4] Check_MK helper [7231]: : >> for sourcehost in os.listdir(dir): 2017-06-06 06:39:36 [4] Check_MK helper [7231]: : >> OSError: [Errno 2] No such file or directory: '/omd/sites/mysite/tmp/check_mk/piggyback/backedhost'

This was some kind of race condition when one Check_MK helper cleaned up outdated piggyback files while another helper was reading the piggyback data.

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