**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
Dan O'Brien
Mike Eves
KUOKA Yusuke
Cedric Meury