[pipeline] Quagga moved to passive support, MPLS and dockerfile changes for the pipeline

quagga: feature moved to passive support

NeST passively supports quagga because it is no longer maintained by the quagga community. FRR is the new default routing_suite.

Affected files and features:

• config.json
• Corresponding READMEs and comments
• coverage and pytest parameters

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dockerfile: bump up ubuntu and docker versions

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routing: retracted examples from pipelne

The outcomes of the dynamic routing examples are unpredictable. Hence, skipping these examples from being run in pipeline.

Affected files and features:

• coverage and pytest parameters