ClearCase: Handle read-only view private files

View private files have state NotManaged. In the corner case
where a NotManaged file is read-only they should be made
writeable by the ReadOnlyFilesDialog, and not vcsOpen()-ed.

Change-Id: Icfeab6bebb76cc01da693b3bfff7b46c45b106b4
Reviewed-by: Orgad Shaneh <orgads@gmail.com>