Fix downloader

[fvoges]

This patch changes two things in install.pp

• Switches the download tool from wget to curl to allow the use of
  the 'file://' scheme for the download URL (wget doesn't support file://)
• Checks $::gitlab::puppet_manage_packages before declaring
  Package['curl']. This follows the behaviour of the other dependencies
  and Puppet best practices.

[spuder]

Thanks for the merge request. I've noticed that the gitlab download page recommends using wget for the ubuntu packages, but curl for the centos packages.

Before this gets merged, I'd like to consider the following:

• Will this have any negative side affects for ubuntu users?
• Does curl have a timeout option? see issue Timeout and https issue for download #82
• Add documentation to readme showing file:// syntax.

[fvoges]

curl has options to set timeouts:

--connect-timeout <seconds>
    Maximum time in seconds that you allow the connection to the server to take.  This only limits the
    connection phase, once curl has connected this option is of no more use. See also the -m/--max-time option.
-m/--max-time <seconds>
    Maximum time in seconds that you allow the whole operation to take.  This is useful for preventing
    your batch  jobs  from  hanging for hours due to slow networks or links going down.  See also 
    the --connect-timeout option.

[binford2k]

why not nanliu/staging?

[fvoges]

The latest commits moved the package declaration to packages.pp as requested

[igalic]

this has been sitting around for long enough that gitlab has made it obsolete by now offering apt/yum repositories.