Add ingestion of VMCATCHER_EVENT_AD_MPURI

As per https://github.com/hepix-virtualisation/vmcatcher/pull/8 , vmcatcher now provides also the image marketplace uri under the variable VMCATCHER_EVENT_AD_MPURI . This patch is to add this information into the OpenNebula image template, for two reason:
 1. Identifying the marketplace source of an image
 2. Have the marketplace information in the middleware to fill the BDII
Fallback for no description

If no description is provided by vmcatcher (eg. no description is present into the imagelist), then fallback to use the title as image description
Merge pull request #10 from spinto/patch-1

Add ingestion of VMCATCHER_EVENT_AD_MPURI
Merge pull request #11 from spinto/patch-2

Fallback for no description
Releasing OpenNebula vmcatcher_eventHndlExpl_ON-0.0.8 release with the changes introduced by Salvatore Pinto
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