Attempt to fix apt repo key error

I was getting the following apt package authentication error:

    WARNING: The following packages cannot be authenticated!
      mapr-core mapr-fileserver mapr-cldb
    STDERR: E: There are problems and -y was used without --force-yes

So I figured the problem was to add the mapr repo gnupg key to the apt keyring (this pull request).  However, it appears that this still didn't fix the problem, and I'm getting the same error.

I checked that the key was indeed getting downloaded and added to the apt keyring, and that it was correct:

    vagrant@nodeX:/var/chef/cache$ sudo apt-get -q -y install mapr-cldb=3.0.2.22510.GA-1
    sudo: unable to resolve host nodeX
    Reading package lists...
    Building dependency tree...
    Reading state information...
    The following extra packages will be installed:
      libcrypt-passwdmd5-perl mapr-core mapr-fileserver mtools sdparm syslinux syslinux-common
    Suggested packages:
      floppyd
    The following NEW packages will be installed:
      libcrypt-passwdmd5-perl mapr-cldb mapr-core mapr-fileserver mtools sdparm syslinux syslinux-common
    0 upgraded, 8 newly installed, 0 to remove and 63 not upgraded.
    Need to get 269 MB of archives.
    After this operation, 4,188 kB of additional disk space will be used.
    WARNING: The following packages cannot be authenticated!
      mapr-core mapr-fileserver mapr-cldb
    E: There are problems and -y was used without --force-yes
    

    vagrant@nodeX:/var/chef/cache$ sudo apt-key update
    sudo: unable to resolve host nodeX
    gpg: key 437D05B5: "Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>" not changed
    gpg: key FBB75451: "Ubuntu CD Image Automatic Signing Key <cdimage@ubuntu.com>" not changed
    gpg: key C0B21F32: "Ubuntu Archive Automatic Signing Key (2012) <ftpmaster@ubuntu.com>" not changed
    gpg: key EFE21092: "Ubuntu CD Image Automatic Signing Key (2012) <cdimage@ubuntu.com>" not changed
    gpg: Total number processed: 4
    gpg:              unchanged: 4
    vagrant@nodeX:/var/chef/cache$ sudo apt-key list
    sudo: unable to resolve host nodeX
    /etc/apt/trusted.gpg
    --------------------
    pub   1024D/437D05B5 2004-09-12
    uid                  Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>
    sub   2048g/79164387 2004-09-12

    pub   1024D/FBB75451 2004-12-30
    uid                  Ubuntu CD Image Automatic Signing Key <cdimage@ubuntu.com>

    pub   4096R/C0B21F32 2012-05-11
    uid                  Ubuntu Archive Automatic Signing Key (2012) <ftpmaster@ubuntu.com>

    pub   4096R/EFE21092 2012-05-11
    uid                  Ubuntu CD Image Automatic Signing Key (2012) <cdimage@ubuntu.com>

    pub   2048R/D2051F97 2014-05-06
    uid                  MapR Technologies, Inc. Linux Package Signing Key (2014) <support@mapr.com>
    sub   2048R/DE308A91 2014-05-06

    
    vagrant@nodeX:/var/chef/cache$ curl -Ls http://package.mapr.com/releases/pub/gnugpg.key | shasum -a 256 | sed -e 's/-/gnugpg.key/' | (cd /var/chef/cache/ && shasum -a 256 -c - )
    gnugpg.key: OK


I think that the real problem was that the MapR packages in the repo are not really signed via gnupg.  I can tell this because there is no `Release.gpg` here: http://package.mapr.com/releases/v3.0.2/ubuntu/dists/mapr/

Compare this to an official Ubuntu Repo: http://us.archive.ubuntu.com/ubuntu/dists/precise/

If it helps, [this Debian Wiki Page][1] explains how apt determines if a package is securely signed, and also how to set up a secure apt repository with a signed `Release.gpg` file.  If there is already some package release script to publish new mapr releases to the repo, it might make things easier just to add the gpg signing step there.

Not sure if you're the right contact to send this to, but I figured I might as well provide this pull request along with some helpful info.

## Steps to Reproduce

    git clone https://github.com/trinitronx/mapr_cookbooks.git
    cd mapr_cookbooks
    git checkout develop
    ./package
    ruby -rjson -e "cluster_json = JSON.load(File.open('install_mapr/fabric/cluster.json.example','r').read); cluster_json['mapr']['nodes'] = []; File.open('install_mapr/fabric/cluster.json','w').write(JSON.pretty_generate(cluster_json))"
    vagrant up

[1]: https://wiki.debian.org/SecureApt