Set default log formatting to use RFC3339Nano with fixed width

[thaJeztah]

This patch changes the logs format to use a fixed-width timestamp, matching the format that's used in dockerd.

Before:

$ containerd
INFO[0000] starting containerd                           revision=a88b6319614de846458750ff882723479ca7b1a1 version=v1.1.0-202-ga88b6319
INFO[0000] loading plugin "io.containerd.content.v1.content"...  type=io.containerd.content.v1
INFO[0000] loading plugin "io.containerd.snapshotter.v1.btrfs"...  type=io.containerd.snapshotter.v1
WARN[0000] failed to load plugin io.containerd.snapshotter.v1.btrfs  error="path /var/lib/containerd/io.containerd.snapshotter.v1.btrfs must be a btrfs filesystem to be used with the btrfs snapshotter"

After:

$ containerd
INFO[2018-07-24T08:11:07.397856489Z] starting containerd                           revision=c3195155cacb361cd3549c4d78901b20aa19579a version=v1.1.0-203-gc3195155
INFO[2018-07-24T08:11:07.399264587Z] loading plugin "io.containerd.content.v1.content"...  type=io.containerd.content.v1
INFO[2018-07-24T08:11:07.399343959Z] loading plugin "io.containerd.snapshotter.v1.btrfs"...  type=io.containerd.snapshotter.v1
WARN[2018-07-24T08:11:07.399474423Z] failed to load plugin io.containerd.snapshotter.v1.btrfs  error="path /var/lib/containerd/io.containerd.snapshotter.v1.btrfs must be a btrfs filesystem to be used with the btrfs snapshotter"

Or, when running as child-process of dockerd:

Before:

$ dockerd --debug
DEBU[2018-07-24T08:15:16.946312436Z] Listener created for HTTP on unix (/var/run/docker.sock)
INFO[2018-07-24T08:15:16.947086499Z] libcontainerd: started new docker-containerd process  pid=231
INFO[2018-07-24T08:15:16.947137166Z] parsed scheme: "unix"                         module=grpc
INFO[2018-07-24T08:15:16.947235001Z] scheme "unix" not registered, fallback to default scheme  module=grpc
INFO[2018-07-24T08:15:16.947463403Z] ccResolverWrapper: sending new addresses to cc: [{unix:///var/run/docker/containerd/docker-containerd.sock 0  <nil>}]  module=grpc
INFO[2018-07-24T08:15:16.947505954Z] ClientConn switching balancer to "pick_first"  module=grpc
INFO[2018-07-24T08:15:16.947717368Z] pickfirstBalancer: HandleSubConnStateChange: 0xc420507ab0, CONNECTING  module=grpc
INFO[0000] starting containerd                           revision=d64c661f1d51c48782c9cec8fda7604785f93587 version=v1.1.1
DEBU[0000] changing OOM score to -500
INFO[0000] loading plugin "io.containerd.content.v1.content"...  type=io.containerd.content.v1
INFO[0000] loading plugin "io.containerd.snapshotter.v1.btrfs"...  type=io.containerd.snapshotter.v1
WARN[0000] failed to load plugin io.containerd.snapshotter.v1.btrfs  error="path /var/lib/docker/containerd/daemon/io.containerd.snapshotter.v1.btrfs must be a btrfs filesystem to be used with the btrfs snapshotter"

After:

$ dockerd --debug
DEBU[2018-07-24T08:21:33.441741970Z] Listener created for HTTP on unix (/var/run/docker.sock)
INFO[2018-07-24T08:21:33.442428017Z] libcontainerd: started new docker-containerd process  pid=232
INFO[2018-07-24T08:21:33.442510827Z] parsed scheme: "unix"                         module=grpc
INFO[2018-07-24T08:21:33.442598812Z] scheme "unix" not registered, fallback to default scheme  module=grpc
INFO[2018-07-24T08:21:33.442681006Z] ccResolverWrapper: sending new addresses to cc: [{unix:///var/run/docker/containerd/docker-containerd.sock 0  <nil>}]  module=grpc
INFO[2018-07-24T08:21:33.442770353Z] ClientConn switching balancer to "pick_first"  module=grpc
INFO[2018-07-24T08:21:33.442871502Z] pickfirstBalancer: HandleSubConnStateChange: 0xc42018bc30, CONNECTING  module=grpc
INFO[2018-07-24T08:21:33.457963804Z] starting containerd                           revision=597dd082e37f8bc6b6265ca05839d7a300861911 version=597dd082
DEBU[2018-07-24T08:21:33.458113301Z] changing OOM score to -500
INFO[2018-07-24T08:21:33.458474842Z] loading plugin "io.containerd.content.v1.content"...  type=io.containerd.content.v1
INFO[2018-07-24T08:21:33.458911054Z] loading plugin "io.containerd.snapshotter.v1.btrfs"...  type=io.containerd.snapshotter.v1
WARN[2018-07-24T08:21:33.459366268Z] failed to load plugin io.containerd.snapshotter.v1.btrfs  error="path /var/lib/docker/containerd/daemon/io.containerd.snapshotter.v1.btrfs must be a btrfs filesystem to be used with the btrfs snapshotter"

[thaJeztah]

Possibly this was "by design", but it kept annoying me to read the logs when containerd was running as child-process of dockerd, and I had this branch still around 😅

[codecov-io]

Codecov Report

Merging #2490 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2490   +/-   ##
=======================================
  Coverage   44.76%   44.76%           
=======================================
  Files          93       93           
  Lines        9555     9555           
=======================================
  Hits         4277     4277           
  Misses       4585     4585           
  Partials      693      693

Flag	Coverage Δ
#linux	48.98% <ø> (ø)	⬆️
#windows	41.04% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
log/context.go	37.5% <ø> (ø)	⬆️

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[crosbymichael]

LGTM

[mlaventure]

LGTM

I actually have the same change locally 😅