Update nagios-api-initd

Modify some params compatible with nagios configuration in CentOS6 with epel-release-6-8
Implemented hostgroup downtime
Update README to include schedule_hostgroup_downtime
Merge pull request #47 from CTrox/master

Implement Hostgroup downtime
Merge pull request #45 from bhxk/master

Update nagios-api-initd
Merge pull request #1 from zorkian/master

Merge upstream changes