* Various U/X improvements for `helmfile apply`
This improves the U/X of `helmfile apply`, by allowing you to selectively apply sub-helmfiles.
When you have two or more sub-helmfiles processed, typing `n` to cancel the first doesn't automatically stop the whole helmfile execution.
Instead, it proceeds by diffing the next sub-helmfile, and asks you to apply it, which should be what the user would expect.
To support this workflow, I have suppressed useless exec logs, correct exit status when diff exists in sub-helmfiles but not in the parent helmfile, and made the final error message emitted by helmfile better.
More concretely, this moves more output from `helm` to STDERR and the `debug` log-level.
The overall output from `helmfile` should be a bit more cleaner especially for `apply`, `sync`, `diff` and perhaps other `helmfile` sub-commands, too.
For example, when one of release failed, `helmfile`'s final error message now includes the error message from the failed `helm` execution, like seen in the last line:
```
List of updated releases :
RELEASE CHART VERSION
envoy stable/envoy 1.5.0
List of releases in error :
RELEASE
envoy2
in ./helmfile.yaml: in .helmfiles[0]: in /Users/c-ykuoka/helmfile/helmfile.1.yaml: failed processing release envoy2: helm exited with status 1:
Error: UPGRADE FAILED: "envoy2" has no deployed releases
```
This way you can better understand what caused helmfile to finally fail.
`helmfile` has been streaminig a lot of stdout and stderr contents from the `helm` commands regardless of the helmfile's log-level. It has been suppressed by default and moved to the `debug` log-level.
You will see that it helps you focus on what was the cause of a failure.
While working on the above, I found an another bug that made `--detailed-exitcode` useless in some case.
That is, `helmfile diff --detailed-exitcode`, when any diff existed only in sub-helmfiles, has been returning an exit code of `1`. It should return `2` when any release had diff and no release had an error, regardless of the target is a sub-helmfile or a parent helmfile. Why? Because that's what `--detailed-exitcode` meant for!
After this PR gets merged, `helmfile diff --detailed-exitcode` propery return exit code `2` in such cases.
Fixes#543Resolves#540
KUOKA Yusuke
Patrick Valsecchi
Shane Starcher
Cedric Meury