assets on file but not in index will now save to index on submission …

[jsnoble]

…resolves #586

[kstaken]

Integration tests pass. Manual tests pass.

Manual test was to copy the asset directory, remove the asset from the system, put the asset directory back in place and then redeploy the asset ensuring it used the same asset ID.

Log messages in this situation

{"name":"teraslice","hostname":"kteramac.local","pid":95926,"module":"assets_storage","level":30,"msg":"asset: c7809e8fcde24c0df1610d6bb1c6d717270c98a2 exists on disk but not in index, saving asset to index","time":"2017-10-30T18:43:49.240Z","v":0}
{"name":"teraslice","hostname":"kteramac.local","pid":95926,"module":"assets_storage","level":30,"msg":"assets: ieee_oui, id: c7809e8fcde24c0df1610d6bb1c6d717270c98a2 has been saved to elasticsearch","time":"2017-10-30T18:43:49.326Z","v":0}