Make the log output less chatty.

This includes the following changes:

- Log messages about adding a DNS record are shown only if the record
  does not exist already and log messages about removing a DNS record
  are shown only if the DNS record exists. This avoids unnecessary log
  chatter when working with static DNS records defined on the global
  level in a Vagrantfile that contains multiple VMs. Previously log
  messages about those static DNS records would have been shown every
  time a VM was started, now they are only shown when starting the first
  VM.

- Just like most log messages already have been, now log output from the
  DNS resolver logic is prefixed with "[landrush] " as well.

- Removes the following messages which were useful on the first day to
  get insight about what's happening under the covers but are pretty
  useless once you understand how landrush works:

  - "Not an OSX machine, so skipping host DNS resolver config."
  - "there are #{DependentVMs.count} VMs left, leaving DNS server and static entries"
Merge pull request #61 from amfranz/less_chatty_log

Make the log output less chatty.
Move ip address processing from awk to ruby, add spec
Ignore ipv6 addresses, use "IPAddr" ruby library
Add spec for invalid ip addresses
Raise error if "hostname -I" doesn't return addresses
Install bundler 1.5 for vagrant
Minitest::Spec instead of rspec to assert raising error
 Fix spec description
Merge pull request #65 from njam/hostname-ipv4

Ignore IPv6 addresses in read_host_visible_ip_address
switch to assignment style enable

matches more closely with general vagrant styyle

backwards compatible with old methods
Merge pull request #63 from phinze/enable-via-assignment

switch to assignment style enable
Use vagrantcloud box identifier from "hashicorp" in example Vagrantfile
Merge pull request #70 from njam/box-hashicorp

Use vagrantcloud box identifier from "hashicorp" in example Vagrantfile
bump Gemfile vagrant version to 1.6.1
use recommended assignment-style enable in example
cut v0.14.0
Update rubydns to fix IPv6 problems
Merge pull request #73 from ciastek/upgrade-rubydns

Update rubydns to fix IPv6 problems, fixes #33
Bump version to 0.14.1