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The adb_logcat_* scripts are extract attached devices names with
pattern 'w+', but it only works for real devices. Emulated devices
have names in form of 'emulator-5554' and '-' sign is not matched
by 'w+' parrent. This causes to logcat output to be missed while
tests are running

R=frankf@chromium.org, craigdh@chromium.org

TEST=Run tests with only emulators attached, ensure that resulting
log contains logcal output

Review URL: https://codereview.chromium.org/661843003

Cr-Commit-Position: refs/heads/master@{#300242}