serverspec be able to override user for tests

[sarcasticadmin]

Description

Currently we hard code the user: https://github.com/socallinuxexpo/scale-network/blob/dea20470a96eca15eff80379303048a362e4f66b/tests/serverspec/spec/spec_helper.rb#L25-L37

Acceptance Criteria

• user is overridable for serverspec