**Feature**
An additional sub-command to the helmfile binary; helmfile test
**Why**
Helm provides helm test (https://github.com/kubernetes/helm/blob/master/docs/chart_tests.md) as a method to run automated tests post chart install to ensure things are working as they should be.
It would be nice to be able to run something like helmfile test against a particular helmfile in order to run helm tests against all charts/releases defined in the file. Either as part of the sync (i.e. helmfile sync --test) to be ran immediately after the corresponding chart is installed, or as a separate command ran after a sync (i.e. helmfile test).
A chart without tests will exit with a 0 status, so it can be safely ran against any charts.
**Notes**
`--cleanup` (bool) & `--timeout` (default: 300) are available as first class arguments. Additional arguments can be passed to the helm binary as with other sub commands using `--args=`
Resolves#144
`helmfile delete` has been implying `--purge` but it is not the case since this change.
The new behavior is `helmfile delete --purge` to actually purge releases.
Run just `helmfile delete` to delete releases but not purge them.
Resolves#71
This adds `releases[].labels` in which you can set arbitrary number of key-value pairs, so that commands like `helmfile sync --selector key=value` can be used to run the helmfile subcommand against a subnet of declared releases.
`labels` and `selector` are named as such on purpose of being consistent with terminology of Kubernetes and other tools in the K8S ecosystem, including kubectl, stern, helm, and so on.
Resolves#8