Fix a flaky test that failed by race condition
Fix a flaky test that failed by race condition

after alpine-edge latest update, test_it_aborts_on_unknown_push_errors
failed in alpine but ok in ubuntu. It seems the deleting repo function
that used by the test executed faster than before in alpine, which then
cause the "put" failed fast when first pulling the repo.

Making it to sleep 2 second to ensure the "put" finishes the pull first
fix the test.

Signed-off-by: Rui Yang <10d6ef426b5f71d33c3d9e2459db4a0e3700cdde@pivotal.io>

concourse/hg-resource,concourse/hg-resource