Relax accelerometer events norm check

Current accelerometer norm check threshold is tight and cause
unnecessary test flakiness in test environment with small
inevitable vibration (e.g. from people walking by testing
lab).

This CL relax the threshold from 0.5m/s^2 to 1m/s^2.

Test: vts pass
Bug: 62811045
Change-Id: I5d7e736623c892b6e6c9b8ddc5d0f53fa8aaba77
Merged-In: I5d7e736623c892b6e6c9b8ddc5d0f53fa8aaba77