Errors don't set a nonzero exit code

[mon]

This makes it more difficult to detect problems when integrating nrfutil in build systems.

By replacing the current click.echo, return with raise click.Exception, 1 is returned and my build stops as expected. Should I use a more specialised exception class such as click.UsageError?

[bihanssen]

@mon, good point about nonzero exit code.
I believe the more specialized exception classes should be used where appropriate, as click will then try to add context info to the error message.