PhpFpmEnvironment::getEnvironmentVariables refactoring

Summary:
Split PhpFpmEnvironment::getEnvironmentVariables in more discrete methods.

New static methods:

• addTempEnvironmentVariables: add TMP, TEMP, TMPDIR env variable to an array
• addPathEnvironmentVariables: add PATH env variable to an array
• addHardcodedEnvironmentVariables: add both to an array

Test Plan: compare output before and after the change

Reviewers: Kaliiixx

Projects: Nasqueron Docker deployment squad

Differential Revision: http://devcentral.nasqueron.org/D36