allow install script to print error on failed binary download

[tommatime]

Proposed Changes

Currently, when the install script encounters an error downloading a file (either the binary signature or the binary itself), the script either exits with no error message or continues running until the missing file causes another error. This is confusing to the user because it is unclear where or why the script failed. This change fixes the bug and allows the error message to print before exiting.

Types of Changes

Bugfix

Verification

For the positive case, the script should continue with no changes to current functionality.

For the negative case, run the script with a condition that will cause the hash or binary download to fail. For example, I set the INSTALL_K3S_VERSION variable to something that does not exist:

$ INSTALL_K3S_VERSION=fake-version sh install.sh

Which should now log something like this, whereas the error message would not show previously:

[INFO]  Using fake-version as release
[INFO]  Downloading hash https://github.com/k3s-io/k3s/releases/download/fake-version/sha256sum-amd64.txt
[ERROR]  Download failed <-- This is the log that was not showing

Testing

No, if there are integration tests for install.sh please point me in that direction so I can make the update.

Linked Issues

Fixes #1774

User-Facing Change

NONE

Further Comments

When logging $? after the case statement, the result was blank rather than holding the return code for the previous command, which I assume bash interpreted as a 0/success code. This change introduces a $status variable that explicitly stores the exit code, and also cleans up some of the -e and +e logic/adds comments to make sure it is clear why they are being used.

This is my first contribution here, and one of my first ever, so please let me know of any additional changes that may need to be made. Thanks!