Support multiple apache2 versions

[linc01n]

Remove apache2 pinning and wrap it inside a begin...rescue block

Related to #148

/cc @bflad @legal90

[legal90]

LGTM 👍

[legal90]

@linc01n To be honest, this statement looks a bit clearer, IMO:

if node['apache'].attribute?('listen_ports')
  # Compatibility with cookbook 'apache' < 3.2.0
  node.default['apache']['listen_ports'] |= [
    node['confluence']['apache2']['port'],
    node['confluence']['apache2']['ssl']['port']
  ]
else
  node.default['apache']['listen'] |= [
    "*:#{node['stash']['apache2']['port']}",
    "*:#{node['stash']['apache2']['ssl']['port']}"
  ]
end

[linc01n]

I think we should put this part in attributes/default.rb
That's the place we usually handle different versioning stuff.