add docker for redhat
Merge pull request #2649 from tnaoto/plugin-provisioner-docker-redhat

Add plugin docker provisioner for redhat
provisioners/docker: Check if epel-release is installed on RedHat-ian guests before attempting installation [GH-2649]
provisioners/docker: Move DockerConfigureVagrantUser capability up to Linux guests [GH-2649]
provisioners/docker: Display warning in case a version get specified on the Vagrantfile and the guest is a RedHat-ian guest [GH-2649]
Update CHANGELOG
Update CHANGELOG
guests/debian: fix dhcp assigned default to work
core: execute SSH commands in context of login shell [GH-2636]
core: -t/-T work for vagrant ssh -c [GH-2618]
core: put shell quoting into its own util class, it is useful
core: SSHRun uses new ShellQuote util
providers/virtualbox: don't clear /etc/exports on BSDs for NFS [GH-2645]
hosts/bsd: check for exports file issues prior to exporting NFS
commands/ssh: use proper variable
Changed wording to reflect Issue #2632
Merge pull request #2655 from drpebcak/master

core: changed wording to reflect Issue #2632