MOF compiler: Limitation that alias must be defined before its use

[andy-maier]

In the MOF processed by the pywbem MOF compiler, an alias must be defined before it is used.
In DSP0004, no such requirement is documented, so this behavior is considered a limitation.

The pywbem MOF compiler should be improved to lift this limitation.

See issue #1079 for a related limitation. For more background, see issue #853.

[andy-maier]

Considering that the WBEM server can create keys (see issue #1079), implementing this requires reordering the create instance operations in case of forward referencing aliases, so that the instances being referenced are created before the instances referencing them.