Uploading duplicate firmware gives unfriendly error message

[rraub]

Describe the bug
When uploading a firmware build that has already been uploaded successfully, you are given a generic "Unknown error uploading firmware.
" error message rather than a more specific message saying its a duplicate. The logs show

To Reproduce
Steps to reproduce the behavior:

1. Go to the /firmware/upload page
2. Click on the box to upload firmware
3. Select a firmware build
4. upload
5. go back to the /firmware/upload page
6. try and re upload the same firmware that you did in the previous step
7. See error Unknown error uploading firmware.

Expected behavior
A message saying this firmware has already been uploaded, so that I don't think there's something wrong with the firmware build.

Screenshots

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
Error logs observed:

16:00:59.167 [error] pid=<0.1763.0> mfa=NervesHub.Firmwares.create_firmware/3 Error while publishing firmware: #Ecto.Changeset<action: :insert, changes: %{size: 32461873, version: "1.xx", description: "xx", author: "xx", org_id: x, product_id: x, uuid: "x", platform: "x", architecture: "armx, delta_updatable: x, org_key_id: x, upload_metadata: %{"s3_key" => "firmware/x/x.fw"}}, errors: [uuid: {"has already been taken", [constraint: :unique, constraint_name: "firmwares_product_id_uuid_index"]}], data: #NervesHub.Firmwares.Firmware<>, valid?: false>

[joshk]

Thanks for reporting this bug.

I'll work on a test for this and see if we can roll out a fix soon.