test VDIs should default to not sharable

Signed-off-by: John Else <john.else@citrix.com>
Improve readability of VDI allowed_operations test failures

Signed-off-by: John Else <john.else@citrix.com>
Add a case to a unit test

Signed-off-by: John Else <john.else@citrix.com>
Test that concurrent copies are allowed

Signed-off-by: John Else <john.else@citrix.com>