Pull the read() inside the MetricsAsserts

This is a bit less efficient, and opens the door for new logs to
appear between asserts, but it makes it easier to write tests.  Tests
probably don't run long enough to worry about losing logs to
roll-over, and hopefully they're already written to ignore
superfluous logs.

Revert "new reader semantics need an explicit read"
This reverts commit 00afa22a.

Bug: 36437556
Change-Id: I6643500eea8ec70d5300052414a9d45a17210591
Test: mmma -j20 platform_testing/tests/functional/notificationtests && adb install -r -g /mnt/fastroid/master/out/target/product/sailfish/data/app/NotificationFunctionalTests/NotificationFunctionalTests.apk && adb shell am instrument -w -e iterations 1 -e class com.android.notification.functional.NotificationInteractionTests com.android.notification.functional/android.support.test.runner.AndroidJUnitRunner && runtest --path platform_testing/libraries/metrics-helper/tests