Demote system_suspend test to postsubmit

SystemSuspendTest.CleanupOnAbort is flaky b/127310798. Demote the test
from presubmit to postsubmit.

Fixes: 127286160
Test: n/a
Change-Id: I7cb70583fae9292a6f0c4a6fbd63594d42fb2247
1 file changed