introspectionSuite.SetUpTest failure

[Tim Penhey]

When multiple test runs are running on the same physical machine, it is possible
that the abstract domain socket used on the machine is in use.

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FAIL: socket_test.go:57: introspectionSuite.SetUpTest

socket_test.go:68:
    c.Assert(err, jc.ErrorIsNil)
... value *errors.Err = &errors.Err{message:"unable to listen on unix socket", cause:(*net.OpError)(0xc8203ee460), previous:(*net.OpError)(0xc8203ee460), file:"github.com/juju/juju/worker/introspection/socket.go", line:55} ("unable to listen on unix socket: listen unix @introspection-test: bind: address already in use")
... error stack:
 listen unix @introspection-test: bind: address already in use
 github.com/juju/juju/worker/introspection/socket.go:55: unable to listen on unix socket

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PANIC: socket_test.go:89: introspectionSuite.TestCmdLine