Bug1082555-[Video]-Fix of currentVideo getting reset during suspend resume operation r=russn

Thanks John, Updated the PR to reflect your feedback. The entry points for updateLoadingSpinner as you suggested are:
On scan end - 
https://github.com/mozilla-b2g/gaia/blob/master/apps/video/js/db.js#L50
startParsingMetadata -
https://github.com/mozilla-b2g/gaia/blob/master/apps/video/js/metadata.js#L56
processFirstQueuedItem -
https://github.com/mozilla-b2g/gaia/blob/master/apps/video/js/metadata.js#L123

I tested extensively and for this bug, only entry point triggered is once from  scan end. Do you think processingQueue and stopParsingMetadataCallback are the flags that prevent mutiple entries of this function.