Collapses status bar on teardown so it does not affect other tests.

BUG: 30639703

Test: mmm -j32 frameworks/base/packages/Shell && adb install -r -g ${ANDROID_PRODUCT_OUT}/data/app/ShellTests/ShellTests.apk && adb shell am instrument -e class com.android.shell.BugreportReceiverTest -w com.android.shell.tests/android.support.test.runner.AndroidJUnitRunner

Change-Id: I2635439ac0c033d1ad6b4ba545b8d751f5576b72