uninstall chefdk when installing chef-workstation

[mattray]

Older installs may have been using chefdk and this will fail.

Mixlib::ShellOut::ShellCommandFailed
  ------------------------------------
  chef_ingredient[chef-workstation] (managed_chef_server::_workstation line 2) had an error: Mixlib::ShellOut::ShellCommandFailed: yum_package[chef-workstation] (/data-chef/chefrun/.chef/local-mode-cache/cache/cookbooks/chef-ingredient/libraries/default_handler.rb line 55) had an error: Mixlib::ShellOut::ShellCommandFailed: Expected process to exit with [0], but received '1'
  ---- Begin output of ["yum", "-y", "install", "/data-chef/utility/rpms/chef-workstation.rpm"] ----
  STDOUT: Loaded plugins: enabled_repos_upload, package_upload, product-id, search-
                : disabled-repos, subscription-manager
  Examining /data-chef/utility/rpms/chef-workstation.rpm: chef-workstation-20.11.180-1.el7.x86_64
  Marking /data-chef/utility/rpms/chef-workstation.rpm to be installed
  Resolving Dependencies
  --> Running transaction check
  ---> Package chef-workstation.x86_64 0:20.11.180-1.el7 will be installed
  --> Processing Conflict: chef-workstation-20.11.180-1.el7.x86_64 conflicts chefdk
  No package matched to upgrade: chef-workstation
  --> Finished Dependency Resolution
   You could try using --skip-broken to work around the problem
    STDERR: Error: chef-workstation conflicts with chefdk-3.3.23-1.el7.x86_64
  ---- End output of ["yum", "-y", "install", "/data-chef/utility/rpms/chef-workstation.rpm"] ----
  Ran ["yum", "-y", "install", "/data-chef/utility/rpms/chef-workstation.rpm"] returned 1