The value of the `shlib_directory` is dependent the system architecture.
Specifically, x86_64 machines use `/usr/lib64/postfix`, while everything
else uses `/usr/lib/postfix`. This role was originally deployed on a
Raspberry Pi, so the original path was correct. Attempting to deploy it
on an x86_64 machine revealed the error.
This commit adds a new task that loads a variables file based on the
architecture. Each option defines an `arch_libdir` variable, which can
be expanded in the `postfix_shlib_directory` variable as needed.
Dustin C. Hatch
0a975ae4af