Add test to verify successful upload

[aik099]

The test suite doesn't check uploaded file checksum match. It checks only, this:

• the upload happened without errors from the Selenium side;
• the change JS event was triggered.

Need to:

1. add a test, that compares the checksum of the to-be-uploaded file with the file-received-on-web-server.
2. check, that all upload-capable drivers pass this test.

P.S.
Created per @uuf6429 comment (see #88 (comment)).