cache process.env

[tjwebb]

Issue Description

process.env results in an OS call for every access, and can be very slow if called on every request to check environment for some reason. Typical usage should recommend that process.env be only used in the configs (i.e. in the filers under config/) but there could be scenarios where a user may want to access it directly.

Caching it would also allow the system to throw an error if the user (or malicious code) attempts to modify process.env during runtime.

See:

• Cache accesses to process.env? nodejs/node#3104 (comment)
• os: make tmpdir be const value nodejs/node#1648 (comment)
• Cache accesses to process.env? nodejs/node#3104 (comment)

Environment

• node version: all
• trails version: all
• operating system: all