exo: Further improve ignored-by-shelf test.
exo: Further improve ignored-by-shelf test.

Avoid test when we have pending configure requests and never let
the shelf ignore windows unless maximized. This avoids having
the state change twice when a window is being maximized.

BUG=549781
TEST=exo_unittests
TBR=dcastagna@chromium.org

Review URL: https://codereview.chromium.org/1874933002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#386317}

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