Attempt to de-flake testProcessMemorySnapshot

- Move the sleep to before the pull to allow time for pulled information
to be populated.

Fixes: 156691707
Test: atest -rerun-until-failure=20
CtsStatsdHostTestCases: android.cts.statsd.atom.UidAtomTests#testProcessMemorySnapshot
Change-Id: Ia84c1dd5c29873792292bf934036ee93d51b199c