Update check_equallogic.sh

This script need a connectivity check (see tatref's request )

Here is an bugfixe in check disk when name is not resolve :

- Before :
./check_equallogic.sh -C public -H bad_name -t disk
getaddrinfo: bad_name Name or service not known
snmpwalk: Unknown host (bad_name)
DISK OK 0 disks OK 0 disks spare

- After :
./check_equallogic.sh -C public -H bad_name -t disk
getaddrinfo: bad_name Name or service not known
snmpwalk: Unknown host (bad_name)
UNKNOWN: check disk failed, please check your config.