snap build job doesn't properly fail on incorrect shas of downloaded snaps

See for example the log from [this job](https://jenkins.edgexfoundry.org/job/edgex-go-snap-fuji-verify-snap/9/console):

```
22:26:13 sha512sum: WARNING: 1 computed checksum did NOT match
22:26:13 core.snap: FAILED
22:26:13 Parallel unsquashfs: Using 4 processors
22:26:13 Read on filesystem failed because EOF
22:26:13 read_uids_guids: failed to read id index table
22:26:13 FATAL ERROR:failed to uid/gid table
22:26:13 core18.snap: OK
```
the job still goes on to try to run and fails for other unknown reasons.

Start with the Jenkins job linked in the issue and trace the shell commands that verify downloaded snap checksums. Reproduce the shown log, then confirm that an incorrect SHA causes the job to stop before later snap execution; validate the result with the affected job or its available checks.

Written by the indexing model from the issue text.