podman: better error message required in case error in CNI plugin.

Is this a BUG REPORT or FEATURE REQUEST? (leave only one on its own line) /kind bug

Description

In case of any error in CNI config file, the error message while creating container with network of CNI plugin simply show error CNI network "<network-name>" not found. This error message is confusing for end user.

A better error message will be helpful to understand where actually error is.

Raised by podman end user:

Steps to reproduce the issue:

1. Create CNI plugin with some error.

$ cat /etc/cni/net.d/77-ipvlan.conflist 
{
    "cniVersion": "0.3.0",
    "name": "myvlan",
    "plugins": [
      {
        "type": "ipvlan",
        "master": "enp1s0", #some comments
        "ipam": {
            "type": "host-local",
            "subnet": "10.88.0.0/16",
            "routes": [
                { "dst": "0.0.0.0/0" }
            ]
        }
     }
    ]
}

1. create container with myvlan network.

$ sudo podman  run --rm -it --network=myvlan docker.io/library/alpine sh
ERRO[0000] CNI network "myvlan" not found               
Error: error configuring network namespace for container baf2fda585db0cc2c874a4bfc00bca3dd27e8402a18ec8e157124240ca887f29: CNI network "myvlan" not found

1. To understand complete details of error, users has to run podman create with --log-level-debug option.

DEBU[0000] overlay test mount indicated that metacopy is not being used
DEBU[0000] backingFs=extfs, projectQuotaSupported=false, useNativeDiff=true, usingMetacopy=false
WARN[0000] Error loading CNI config list file /etc/cni/net.d/77-ipvlan.conflist: error parsing configuration list: invalid character '#' looking for beginning of object key string
INFO[0000] Found CNI network podman (type=bridge) at /etc/cni/net.d/87-podman-bridge.conflist
WARN[0000] Error loading CNI config file /etc/cni/net.d/97-podman-macvlan.conf: error parsing configuration: missing 'type'
INFO[0000] Found CNI network lo (type=loopback) at /etc/cni/net.d/99-loopback.conf

Describe the results you received:

ERRO[0000] CNI network "myvlan" not found               
Error: error configuring network namespace for container baf2fda585db0cc2c874a4bfc00bca3dd27e8402a18ec8e157124240ca887f29: CNI network "myvlan" not found

Describe the results you expected: A better error message suggesting where error exist.

Additional information you deem important (e.g. issue happens only occasionally):

Output of podman version:

$ podman version
Version:            1.3.0-dev
RemoteAPI Version:  1
Go Version:         go1.12.3
Git Commit:         cb2b019d5debadbe29cba59e93130bd8c562771a-dirty
Built:              Fri Apr 12 10:07:18 2019
OS/Arch:            linux/amd64

Output of podman info --debug:

$ podman info --debug                                                                       
debug:
  compiler: gc
  git commit: cb2b019d5debadbe29cba59e93130bd8c562771a-dirty
  go version: go1.12.3
  podman version: 1.3.0-dev
host:
  BuildahVersion: 1.7.2
  Conmon:
    package: Unknown
    path: /usr/libexec/podman/conmon
    version: 'conmon version 1.14.0-dev, commit: f02fc40ed55504247af4fbf09fd8577d315a6c73'
  Distribution:
    distribution: elementary
    version: "5.0"
  MemFree: 6248939520
  MemTotal: 24985653248
  OCIRuntime:
    package: 'cri-o-runc: /usr/bin/runc'
    path: /usr/bin/runc
    version: 'runc version spec: 1.0.1-dev'
  SwapFree: 2140925952
  SwapTotal: 2147479552
  arch: amd64
  cpus: 8
  hostname: kunal-HP-dev
  kernel: 4.15.0-46-generic
  os: linux
  rootless: true
  uptime: 167h 43m 36.61s (Approximately 6.96 days)
insecure registries:
  registries: []
registries:
  registries:
  - docker.io
  - registry.fedoraproject.org
  - quay.io
  - registry.access.redhat.com
  - registry.centos.org
store:
  ConfigFile: /home/kunal/.config/containers/storage.conf
  ContainerStore:
    number: 0
  GraphDriverName: vfs
  GraphOptions: null
  GraphRoot: /home/kunal/.local/share/containers/storage
  GraphStatus: {}
  ImageStore:
    number: 0
  RunRoot: /run/user/1000/run
  VolumePath: /home/kunal/.local/share/containers/storage/volumes

Additional environment details (AWS, VirtualBox, physical, etc.):