test: Add check for file IO shared pointer

This implies making the RadosFsTest class a friend of RadosFsFile.
Change indexObject's argument to not be a reference

It doesn't make sense because the type in question is just a
void *.
Add lazy removal of shared file instances

If more than one instance of a file exist, then its removal is done
only after all instances cease to exist.
Check for lazy removal when creating a file

Because the file may exist but be marked for lazy removal, in which
case, it should no longer be removed.
test: Add test for lazy removal of a file