Migrate salt.cloud.exceptions to salt.exceptions

This means that we no longer have to load salt.cloud when calling the
salt cli and paves the way for additional sandboxing of salt-cloud to avoid
unecessary imports.
Remove what seem to be unused imports.
Fix tests and lint
Missed one lint
Merge pull request #15479 from cachedout/no_cloud

Migrate salt.cloud.exceptions to salt.exceptions