test: allow common.PIPE to be configured via env
test: allow common.PIPE to be configured via env

Add optional env var $NODE_COMMON_PIPE for setting common.PIPE to
manually deal with maximum path lengths for unix sockets.

PR-URL: https://github.com/node-forward/node/pull/26
Reviewed-By: Ben Noordhuis <59bd0a3ff43b32849b319e645d4798d8a5d1e889@bnoordhuis.nl>

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node