Better error reporting in Crowbar webui

Better error reporting in Crowbar via the web interface to support the user:
The last logged lines of the respective chef client run are now displayed if
a propsal fails.
Add basic checks for machines controller
Replace duplicate code setting name with a before_filter
Load machine in a before filter in MachinesController
Dont duplicate rendering code in every action
Render 404 in a before filter, removing the need for if nil? checks
Make sure the cloud domain is set before each action call
Fix spec - use post to call actions in MachineController
Add check that no op is called when node not found
Rename render_machine to render_empty_json, use explicit render in show
Use flash[:alert] instead of flash[:notice]
Add support for exporting support configs
Add helper for checking if we're running on a suse system
Do not offer supportconfig export if not running on SUSE
Use full report, so it will contain cloud plugin data
Merge pull request #776 from nkrinner/bnc797059-roxy

Better error reporting in Crowbar webui
Use better variable name in suse_system
Remove double call to join
Merge pull request #842 from bkutil/add_supportconfig_export

Add support for exporting support configs
Use JSON response for 404

Update tests to reflect this.