Use MULTUS_MASTER_CNI_FILE_NAME as MASTER_PLUGIN as is, if specified

[cgchinmay]

Before change, specifying MULTUS_MASTER_CNI_FILE_NAME would not properly generate multus conf as the file path was wrong
Multus pod logs would show following error

kubectl logs -f pod/kube-multus-ds-8zs2t -n kube-system
2021-07-12T16:50:00+0000 Generating Multus configuration file using files in /host/etc/cni/net.d...
2021-07-12T16:50:00+0000 Using MASTER_PLUGIN: /host/etc/cni/net.d/10-aws.conflist -> this should take only filename and not entire path 
cat: /host/etc/cni/net.d//host/etc/cni/net.d/10-aws.conflist: No such file or directory -> Incorrect file path 
Traceback (most recent call last):
  File "/tmp/tmp.zngU7gWnzK", line 2, in <module>
    conf = json.load(sys.stdin)
  File "/usr/lib64/python2.7/json/__init__.py", line 290, in load
    **kw)
  File "/usr/lib64/python2.7/json/__init__.py", line 338, in loads
    return _default_decoder.decode(s)
  File "/usr/lib64/python2.7/json/decoder.py", line 366, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib64/python2.7/json/decoder.py", line 384, in raw_decode
    raise ValueError("No JSON object could be decoded")
ValueError: No JSON object could be decoded

After change , multus conf can be correctly generated when MULTUS_MASTER_CNI_FILE_NAME is specified

kubectl logs -f pod/kube-multus-ds-bvdtp -n kube-system
2021-07-12T16:54:22+0000 Generating Multus configuration file using files in /host/etc/cni/net.d...
2021-07-12T16:54:22+0000 Using MASTER_PLUGIN: 10-aws.conflist
2021-07-12T16:54:22+0000 Nested capabilities string: "capabilities": {"portMappings": true},
2021-07-12T16:54:22+0000 Using /host/etc/cni/net.d/10-aws.conflist as a source to generate the Multus configuration
2021-07-12T16:54:22+0000 Config file created @ /host/etc/cni/net.d/00-multus.conf
{ "cniVersion": "0.3.1", "name": "multus-cni-network", "type": "multus", "capabilities": {"portMappings": true}, "kubeconfig": "/etc/cni/net.d/multus.d/multus.kubeconfig", "delegates": [ { "cniVersion": "0.3.1", "name": "aws-cni", "plugins": [ { "name": "aws-cni", "type": "aws-cni", "vethPrefix": "eni", "mtu": "9001", "pluginLogFile": "/var/log/aws-routed-eni/plugin.log", "pluginLogLevel": "DEBUG" }, { "type": "portmap", "capabilities": {"portMappings": true}, "snat": true } ] } ] }
2021-07-12T16:54:22+0000 Entering sleep (success)...

[coveralls]

Pull Request Test Coverage Report for Build 1023717673

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 71.082%

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Totals
Change from base Build 1011872125:	0.0%
Covered Lines:	1143
Relevant Lines:	1608

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💛 - Coveralls

[cgchinmay]

@s1061123 @dougbtv Can one of you review ? Thanks

[dougbtv]

Thanks for identifying this and fixing it up 👍

[LittleFox94]

Any chance to have a new release with this in? Currently being bitten by the problem this fixes

[s1061123]

We'll discuss about it in maintainer's meeting. Let's see...

[dougbtv]

@LittleFox94 thanks for the report! We've released v3.8 @ https://github.com/k8snetworkplumbingwg/multus-cni/releases/tag/v3.8 the image should be building as I type this comment 👍