Update cfme/config/configuration page

Add new, more specific exception

Add set_server_role() func to only enable/disable a single role; not touching/disabling the rest

Add part of config menu

Update minor changes here and there
Fix docs
fix mgmt_system rhev deletes
Merge pull request #586 from jkrocil/doc-update

Fix docs
Merge pull request #587 from jkrocil/cfme-config-update

Update cfme/config/configuration page
Merge pull request #588 from dajohnso/fix_rhev_deletes

fix mgmt_system rhev deletes