Using basic types as values in the `ImageConfig` structure makes it
impossible to distinguish if the empty value for the type was set
intentionally or if it is just the value the variable was initialized
to. This is very bad especially for `bool` type.
While working on unifying `vhd` and `azure-rhui` image types I found
out, that some newly added variables in the `ImageConfig` structure
were forgotten in the `InheritFrom()` method. This makes it impossible
to inherit their values from a parent configuration. This is however
required for the unification of `vhd` and `azure-rhui` image types. As
described above, it would be impossible to decide whether a `bool` value
should be inherited from the parent configuration or not. The only
solution is to use a pointer to the type. For consistency, use pointer
for all basic types.
Adjust distro implementations accordingly.
c8382f1654