bridge: Skip test-metric when PCP can't be initialized
bridge: Skip test-metric when PCP can't be initialized

This might happen when pmcpp is missing, for example, which is in
another package.

See https://github.com/performancecopilot/pcp/issues/2

Closes #1697
Reviewed-by: Stef Walter <8a7fbf0f15d3ad982af54ef28f5c117d2494b76c@redhat.com>

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