Print detailed error when installing package.

[harryge00]

What this PR does / why we need it:

Fixes #1269
Print detailed error when resolver cannot find the specific package or version.

1. When install a non-existent operator version:

# ./bin/kubectl-kudo-original install kafka --operator-version=8.0.0        
Error: failed to resolve operator package for: kafka resolver: unable to find packages for kafka
# ./bin/kubectl-kudo-new-fix install kafka --operator-version=8.0.0    
Error: failed to resolve operator package for: kafka getting kafka in index file: no operator version found for kafka-8.0.0

2. When install a non-existent package

# ./bin/kubectl-kudo-original install non-exist     
Error: failed to resolve operator package for: non-exist resolver: unable to find packages for non-exist
# ./bin/kubectl-kudo-new-fix install non-exist  
Error: failed to resolve operator package for: non-exist getting non-exist in index file: no operator found for: non-exist

[zen-dog]

Lgtm! 🚢

[harryge00]

I just removed resolver: unable to find packages for because it seems a bit duplicate when detailed error is returned.

[kensipe]

noice!