....I..... [RSM-1] improve Name Server availability calculations by introducing parallelization

This commit introduces next changes:
- rsm.slv.dns.ns.avail.pl will run in parallel (64 processes, default)
- the logging is handled by syslog (rsyslog)
- additional rsyslog rules must be integrated (see. Nr. 32 of opt/zabbix/docs/server_install)
- SLV scripts logs path changed from /var/log/zabbix to /var/log/zabbix/slv
- rsm.conf option "logdir = /var/log/zabbix" is now ignored (this part is moved to rsyslog configuration)