Add capability to read resolv.conf for FQDN sysname

[ashish12pant]

- What I did
Read domain name from /etc/resolv.conf and return FQDN value for sysName

- How I did it

• As default behaviour only hostname will be returned. If hostname configured in config_db is FQDN than that value will returned
• If hostname in config_db is not FQDN and If there is a domain name in the /etc/resolv.conf. Domain name is read from the file and FQDN value is returned for sysName.

- How to verify it
snmpget -Oqv -v 2c -c 'public' <ip_address> 1.3.6.1.2.1.1.5.0

- Description for the changelog
Capability to read resolv.conf for FQDN sysname