Do not allow to modify access for public volume type

Do not allow to modify access for public volume type

Now public volume type can be added/removed project access, but when
listing access, cinder returns 'Access list not available for public
volume types.' It's weird for users experience.

We should check if a type is public and do not allow public volume type
to modify project access.

APIImpact
When modifying access for public volume type, API will return 400 and message:
"Invalid volume type: Type access modification is not applicable to public
volume type."

Closes-Bug: #1467808

Change-Id: Id03eb3649ce02549c131c85697d8431c3f8c04dd