fix(core): more detailed error message when version cannot be found

[ghiscoding]

Description

As per Lerna PR 3424

When running a lerna command and no version is present in lerna.json configuration following error message is printed:

lerna ERR! ENOLERNA `lerna.json` does not exist, have you run `lerna init`?

As described in (lerna/lerna#3311) this is not completely correct.

Additional check is added during command validation to prove a version is available in lerna.json file. In addition the check for having a lerna configuration (lerna.json) available is adapted to really check for existance of the config file. This is achieved by setting an additional flag configNotFound in the project object during lerna.json retrival.

Motivation and Context

Improve error messages for invalid lerna.json to support user finding configuration problems. The issue is described here (lerna/lerna#3311).

How Has This Been Tested?

Added a unit test. Manually built a lerna version.

Types of changes

• Chore (change that has absolutely no effect on users)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.