Copy to VAST success message is misleading when extending expiration dates

[pgarrison]

Steps to reproduce:

• Select a file that is already on the VAST
• Right click -> Copy to VAST
• Check that the file is going to have its expiration date extended
• Click confirm
• Actual behavior: Success message says that "files were successfully queued for download" (see screenshot)
• Expected behavior: Success message says that the VAST reservation was extended

It's a little less clear what should happen when some files are queued for download and some have their expiration extended. Perhaps the modal just mentions the ones queued for download? E.g., if 10 files are selected and 4 need to be downloaded, the text is "4 out of 4 files were successfully queued for download..."