Do not raise an exception if an empty/invalid box dir is found
Optionally show progress when importing remote OVA/box

Kinda useful when downloading large boxes/OVAs from remote servers:

    octoc = Fog::Compute.new( :provider => 'octocloud' )
    cube = octoc.cubes.create :name => 'test-cube',
                              :source => "https://foo.bar.com/myova.ova",
                              :extra_opts => { :show_progress => true }

When the progressbar gem is available, it will automatically use it:

    Downloading:    16% |ooooooooooooooo   |   1.2MB 331.8KB/s ETA:   0:00:19

Gracefully degrades to a simple download animation otherwise:

    Downloading... 7.68 MB
Added extend_expiry method to the Server model

Added to Server instead of RemoteServer so we have the same public
interface in both Local and Remote servers.
The method returns false when using the local Fusion driver.
Merge pull request #16 from rubiojr/server-extend-expiry

Added extend_expiry method to the Server model
Merge pull request #14 from rubiojr/local-list-boxes-fixes

Do not raise an exception if an empty/invalid box dir is found
Merge pull request #15 from rubiojr/box-ova-import-progressbar

Optionally show progress when importing remote OVA/box