Allow for usage of a corporate package repo and key server.

[minishri9]

Hi Christoph and Alex,

We have "new secure VLAN" templates for the pipeline hosts which I am currently testing. These have no access to download anything from the internet. Therefore we had to modify the dashboard cookbook so that there is no dependency at all on any external repository, this includes the Ubuntu key-server. One piece of this task, was that the dash-debian-repo recipe in chef-dash which contacts the Ubuntu key server also had to be changed. After discussing, we decided to make chef-dash more flexible to allow usage of a corporate repo to install dashboard packages. We will add the dash packages key via "apt-key add" if using a corporate repo. So,

1. Introduce an attribute "use-corp-repo" which can be set to "true" or "false". Defaults to "false" to use the Pingworks repo and Ubuntu key server. if set to "true" downloads the dashboard packages (scripts, front-end and back-end) from the corporate repo and provisions the dash packages key from a cookbook file using "apt-key add".
2. However this means we have to also move the install_method choice over to chef-dash. So I will introduce a case statement on the value of the "use-corp-repo" attribute, which sets the install_method to "dpkg" when "use-corp-repo" is "true" and sets it to "apt" when it is "false"
3. This means splitting all package installation recipes into two choices for "dpkg" and "apt" install methods based on the value of "use-corp-repo".