This was a test for a 13 year old problem to do with problems
launching libguestfs appliances in parallel. That problem does not
affect current code.
Testing build/launch of libguestfs appliances is a valuable thing to
test. However we start libguestfs in parallel in both the current
test suite and in higher level tools, and this test was dubious (and
breaks with recent changes). Therefore remove the test.
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