Extend & refactor Statsd TestDrive tool.

Now allows capturing multiple events under the same event metric.
Added unit tests for configuration generation and command-line
interpretation.  Refactored configuration into an inner class and
added functionality using TDD.

Also updated TestDrive & LocalDrive tools to check ANDROID_SERIAL as well as
the -s parameter when multiple devices are connected, and improved error messages.

Bug: 149914234
Test: atest --host test/com/android/statsd/shelltools/testdrive/*.java
Test: out/host/linux-x86/bin/statsd_testdrive -s <SERIAL> 90
Test: out/host/linux-x86/bin/statsd_localdrive -s <SERIAL> get-data 90
Change-Id: I4e756c2b132a22d66ccaf7b3346fe4fbf1f6f1fb