(MCOP-13) Puppet Agent should validate IPs as names

Enabling the validation of IPv4 and IPv6 addresses in the server
validator of the Puppet Agent; updating the related spec tests.

IP addreesses can be valid host names. We now consider IPv4 and IPv6
addresses when parsing and validating server names by using the ipaddr
library.
The validation code has been refactored in puppet_server_address_validation.rb
(shared by the validator, in puppet_agent_mgr.rb, and the agent,
in puppet_agent_mgr/common.rb).