logcat: test: inject messages if necessary for tail test requirements

For the gTests logcat.tz, logcat.tail_3, logcat.tail_10,
logcat.tail_100, logcat.tail_1000 and logcat.tail_time tests inject
messages if we come up short should the background logging not be
sufficient to feed the test requirements.  Test frames run the
tests right after reboot requiring injection.  Will have radio
silence, so we also add kernel logs if available to help add to the
background logging activity level.

We also will inject a radio message for logcat.buckets so that test
can survive no radio content.

Test: set device to airplane mode (to stress this problem) then:
      adb logcat -b all -c && adb shell su root \
          /data/nativetest/logcat-unit-tests/logcat-unit-tests \
          --gtest_filter=logcat.tail_1000 (or others in this set)
Bug: 34454772
Change-Id: I5ec246552f3ab1fc9c5864ed69d63b851fdf538d