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!)
Peter Rifel