./run.sh test should terminate when test files download failed

## Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
`./run.sh test`

2. What did you expect to see?
All unit tests passed.

3. What did you see instead?
Some unit tests failed, because some dependent test files download failed.
There are some output:
```
...
Connecting to github-production-release-asset-2e65be.s3.amazonaws.com (github-production-release-asset-2e65be.s3.amazonaws.com)|52.216.138.19|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 962466 (940K) [application/octet-stream]
Saving to: ‘pegasus-bulk-load-function-test-files.zip’

2% [===> ] 25,949 284B/s in 91s

2020-11-21 22:22:07 (284 B/s) - Read error at byte 25949/962466 (Connection reset by peer). Archive: pegasus-bulk-load-function-test-files.zip
End-of-central-directory signature not found. Either this file is not
a zipfile, or it constitutes one disk of a multi-part archive. In the
latter case the central directory and zipfile comment will be found on
the last disk(s) of this archive.
unzip: cannot find zipfile directory in one of pegasus-bulk-load-function-test-files.zip or
pegasus-bulk-load-function-test-files.zip.zip, and cannot find pegasus-bulk-load-function-test-files.zip.ZIP, period.
Prepare files used for bulk load function test succeed
Test start time: Sat Nov 21 22:22:07 CST 2020
...
```

4. What version of Pegasus are you using?
tag 2.1.0-RC5

Start with ./run.sh and follow the test-file download step invoked by ./run.sh test. Reproduce the failed download shown in the report, then verify that the test command terminates instead of continuing to run unit tests. Done means download failures cause the command to stop and report failure.

Written by the indexing model from the issue text.