make cached pillars use pillarenv rather than saltenv

[The-Loeki]

What does this PR do?

when pillar_cache is True, the pillarenv args stop working.
This fixes the problem for me, but I'm unsure about the further ramifications.

What issues does this PR fix or reference?

fixes #42393
which is probably a duplicate of #36153

Previous / New Behavior

I did a search & replace in the affected function saltenv > pillarenv

[ghost]

@The-Loeki, thanks for your PR! By analyzing the history of the files in this pull request, we identified @cachedout, @terminalmage and @thatch45 to be potential reviewers.

[cachedout]

@terminalmage Can you help review this one?

[terminalmage]

I've not dealt much with the pillar cache feature, but the default value for pillarenv is None. I would assume that this would still work, since None is a hashable value and thus could occupy a spot in the cache dict. @The-Loeki have you tested this without explicitly defining the pillarenv to make sure it works? I'm particularly interested in the debug logging that will show what the cache dict looks like.

[The-Loeki]

@terminalmage good point! I hadn't considered it, but as you suspect turns out it 'just works':
However, continuing on that line of reasoning, suppose someone activates one of the external caches, say Redis? Does the same apply?

2017-09-22 23:16:29,951 [salt.pillar      :245 ][DEBUG   ][2294] Pillar cache hit for minion minion.example.net and pillarenv None
2017-09-22 23:16:29,960 [salt.loaded.int.rawmodule.state:2000][DEBUG   ][13145] Remaining event matches: -1095
2017-09-22 23:16:29,963 [salt.utils.reactor:88  ][DEBUG   ][2049] Gathering reactors for tag minion/refresh/minion.example.net
2017-09-22 23:16:30,149 [salt.pillar      :50  ][DEBUG   ][2322] Determining pillar cache
2017-09-22 23:16:30,151 [salt.pillar      :52  ][INFO    ][2322] Compiling pillar from cache
2017-09-22 23:16:30,152 [salt.pillar      :53  ][DEBUG   ][2322] get_pillar using pillar cache with ext: None
2017-09-22 23:16:30,153 [salt.utils.cache :36  ][INFO    ][2322] Factory backend: disk
2017-09-22 23:16:30,156 [salt.pillar      :238 ][DEBUG   ][2322] Scanning pillar cache for information about minion minion.example.net and
 pillarenv None
2017-09-22 23:16:30,158 [salt.pillar      :239 ][DEBUG   ][2322] Scanning cache: {'minion.example.net': {None: {'s3.key': <<lots more stuff that should be in a pillar and therefore not here ;) >>

[terminalmage]

They all use the same dictionary structure, if I understand correctly. @cachedout can you sanity-check me here?