Refactor config - rewrite handling of "reconf"

The way the "reconf"/"reconfigure" argument is handled is overly
complicated.  Just grep for it first, and if it is there in the
current arguments, get the old command line arguments from Makefile.

While we're at it, make the Makefile variable CONFIGURE_ARGS hold the
value as a perl list of strings.  This makes things much safer in case
one of the arguments would contain a space.  Since CONFIGURE_ARGS is
used for nothing else, there's no harm in this.

Reviewed-by: Viktor Dukhovni <viktor@openssl.org>