Add option to set icinga reported hostname to send_ok_to_icinga.sh script

Icinga does not expect FDQNs of hosts.  This changes the default
reported host of this script to just 'analytics1027', and also adds
the ability to set the reported host via the CLI.

Change-Id: I7b27901062f62d23c9c7434e6cbcdb2efd9216b6