We let the addon specify exactly what should be pruned; this approach
is a little more verbose but we're likely generating this
automatically in the common case anyway.
In return for the verbosity, we can likely handle more future cases
and edge cases (for example removing objects that aren't labelled or
are in the wrong namespace).
This removes a redundant printing of error messages and no longer prints the usage help text when channels fails.
Before:
```
NAME CURRENT UPDATE
core.addons.k8s.io - 1.4.0
dns-controller.addons.k8s.io - 1.19.0-alpha.4
kops-controller.addons.k8s.io - 1.19.0-alpha.4
kube-dns.addons.k8s.io - 1.15.13-kops.3
kubelet-api.rbac.addons.k8s.io - v0.0.1
limit-range.addons.k8s.io - 1.5.0
storage-aws.addons.k8s.io - 1.15.0
I1018 16:49:43.908920 87960 addon.go:140] Applying update from "kops/upup/pkg/fi/cloudup/tests/bootstrapchannelbuilder/simple/dns-controller.addons.k8s.io/k8s-1.12.yaml"
Error: error updating "dns-controller.addons.k8s.io": error applying update from "kops/upup/pkg/fi/cloudup/tests/bootstrapchannelbuilder/simple/dns-controller.addons.k8s.io/k8s-1.12.yaml": error reading manifest: open kops/upup/pkg/fi/cloudup/tests/bootstrapchannelbuilder/simple/dns-controller.addons.k8s.io/k8s-1.12.yaml: no such file or directory
Usage:
channels apply channel [flags]
Flags:
-f, --filename strings Apply from a local file
-h, --help help for channel
--yes Apply update
Global Flags:
--add_dir_header If true, adds the file directory to the header of the log messages
--alsologtostderr log to standard error as well as files
--config string config file (default is $HOME/.channels.yaml)
--log_backtrace_at traceLocation when logging hits line file:N, emit a stack trace (default :0)
--log_dir string If non-empty, write log files in this directory
--log_file string If non-empty, use this log file
--log_file_max_size uint Defines the maximum size a log file can grow to. Unit is megabytes. If the value is 0, the maximum file size is unlimited. (default 1800)
--logtostderr log to standard error instead of files (default true)
--skip_headers If true, avoid header prefixes in the log messages
--skip_log_headers If true, avoid headers when opening log files
--stderrthreshold severity logs at or above this threshold go to stderr (default 2)
-v, --v Level number for the log level verbosity
--vmodule moduleSpec comma-separated list of pattern=N settings for file-filtered logging
error updating "dns-controller.addons.k8s.io": error applying update from "kops/upup/pkg/fi/cloudup/tests/bootstrapchannelbuilder/simple/dns-controller.addons.k8s.io/k8s-1.12.yaml": error reading manifest: open kops/upup/pkg/fi/cloudup/tests/bootstrapchannelbuilder/simple/dns-controller.addons.k8s.io/k8s-1.12.yaml: no such file or directory
```
After:
```
NAME CURRENT UPDATE
core.addons.k8s.io - 1.4.0
dns-controller.addons.k8s.io - 1.19.0-alpha.4
kops-controller.addons.k8s.io - 1.19.0-alpha.4
kube-dns.addons.k8s.io - 1.15.13-kops.3
kubelet-api.rbac.addons.k8s.io - v0.0.1
limit-range.addons.k8s.io - 1.5.0
storage-aws.addons.k8s.io - 1.15.0
I1018 16:51:08.918451 88636 addon.go:140] Applying update from "kops/upup/pkg/fi/cloudup/tests/bootstrapchannelbuilder/simple/core.addons.k8s.io/v1.4.0.yaml"
error updating "core.addons.k8s.io": error applying update from "kops/upup/pkg/fi/cloudup/tests/bootstrapchannelbuilder/simple/core.addons.k8s.io/v1.4.0.yaml": error reading manifest: open kops/upup/pkg/fi/cloudup/tests/bootstrapchannelbuilder/simple/core.addons.k8s.io/v1.4.0.yaml: no such file or directory
```
The client-go signature for most methods adds a context.Context
object, and also makes Options mandatory. Feed through a
context.Context through many of our methods (but use context.TODO to
stop it getting totally out of hand!)
Ole Markus With