--env-file does not expose variables to detect

[nebhale]

In the latest revision of the spec, environment variables are exposed during detection. At the moment, these environment variable are only exposed during the build phase. They should be exposed during the detect phase as well.

[sclevine]

Looks good:

liberty:pack pivotal$ ./pack-676-osx build myapp --builder packs/samples:0.0.1-rc.490 --buildpack ./test-bp/ --env-file <(echo 'TESTME=pass')
Defaulting app directory to current working directory /Users/pivotal/workspace/cncf-buildpacks/pack (use --path to override)
Using user-provided builder image packs/samples:0.0.1-rc.490
Pulling builder image packs/samples:0.0.1-rc.490 (use --no-pull flag to skip this step)
Selected run image packs/run:v3alpha2 from stack io.buildpacks.stacks.bionic
Pulling run image packs/run:v3alpha2 (use --no-pull flag to skip this step)
Using cache volume pack-cache-7bae996a0e238a80f14b74a61e3178bf
===> DETECTING
Using manually-provided group
[detector] 2019/01/04 16:01:59 Trying group of 1...
[detector] 2019/01/04 16:01:59 ======== Output:  ========
[detector]
[detector] 2019/01/04 16:01:59 ======== Results ========
[detector] 2019/01/04 16:01:59 : pass

[ekcasey]

released in pack v0.0.9