adds options for client certs to downloader class

Adds :client_cert to the env array and then passes it into the curl
options array
adds param for client certs

adds an option to the command parser for client certicates
adds client cert
adds client cert to default config
adds accessor for client_cert
passes client cert option from Vagrant file to box_add
Merge branch 'master' into client-certs
implemetn array arguments from #1569
Fixed fqdn handling on debian/ubuntu

The issue was that the old method simply didn't work.  When the hosts
file should look like:
    127.0.1.1   host.fqdn.com host
It looked like:
    127.0.1.1   host.fqdn.com host old.fqdn.com old
Or this if the user didn't set a fqdn
    127.0.1.1   host host old.fqdn.com old

This patch fixes that.
check ENV for VAGRANT_NOCOLOR (equivalent of --no-color on cmdline)
Allow to change the DHCP_HOSTNAME on RedHat
Merge pull request #2267 from fcharlier/fcharlier/dhcp_hostname_redhat

guests/redhat: Allow to change the DHCP_HOSTNAME on RedHat
Update CHANGELOG
Merge pull request #2254 from Caustic/fix-hostname-debian

guests/debian,ubuntu: Fixed fqdn handling
Update CHANGELOG
website/docs: mention installing virtualbox
add cfengine provisioner suse install support
Resolving #2194 (Ansible buffering output if run as subprocess)
fixed a broken link
Merge pull request #2284 from jeremyquinton/link_fix

website/docs: fixed a broken link