Add optional support for specifying a NUMA policy

Provides a cleaner mechanism for specifying a NUMA policy when starting an Erlang VM.  

By default, no NUMA policy changes are implemented and numactl will not be executed, so systems that do not support NUMA will be unaffected.

To change the default NUMA policy, the user may edit env.sh and change the NUMACTL_ARG variable to include numactl parameters.  

Example:
NUMACTL_ARG="--interleave=all"

If a user specifies a numactl arg but numactl is not installed/available, then an error is thrown.