AcpiExec/AcpiNames: Update initialization sequence.

Always initialize ACPICA first, before any argument processing.
Otherwise, the output file handle will not be initialized via
AcpiOsInitialize.
Disassembler: Cleanup for parent Op extraction.

Small cleanup for extracting and using a parent Op in a block
of code. Also added comment that explains that the parent
is guaranteed to be valid in this case. ACPICA BZ 1069.