Now treating empty log file as new log file in test.

Testing Done:
Gradle clean build.

Tested with the isolated scheduler and an empty log file.
?  git:(master) ? ls -lh /tmp/testing_log_file                                                                                                          ~/workspace/incubator-aurora
-rw-r--r--  1 skarumuri  wheel     0B Dec 13 14:56 /tmp/testing_log_file

Ran it on master:

Running on an empty file would result in an exception as follows:

E1213 22:58:26.660 THREAD1 org.apache.zookeeper.server.NIOServerCnxn$Factory$1.uncaughtException: Thread Thread[main,5,main] died
java.lang.IllegalStateException: Failed to open the log, cannot continue
	at com.twitter.aurora.scheduler.storage.log.LogStorage.prepare(LogStorage.java:289)
	at com.twitter.aurora.scheduler.storage.CallOrderEnforcingStorage.prepare(CallOrderEnforcingStorage.java:80)
	at com.twitter.aurora.scheduler.SchedulerLifecycle.prepare(SchedulerLifecycle.java:144)
	at com.twitter.aurora.scheduler.app.SchedulerMain.run(SchedulerMain.java:255)
	at com.twitter.common.application.AppLauncher.run(AppLauncher.java:102)
	at com.twitter.common.application.AppLauncher.launch(AppLauncher.java:181)
	at com.twitter.common.application.AppLauncher.launch(AppLauncher.java:142)
	at com.twitter.aurora.scheduler.app.SchedulerMain.main(SchedulerMain.java:276)
Caused by: java.io.IOException: Failed to interpret log contents: com.twitter.aurora.codec.ThriftBinaryCodec$CodingException: Failed to deserialize thrift object.
	at com.twitter.aurora.scheduler.log.testing.FileLog.open(FileLog.java:80)
	at com.twitter.aurora.scheduler.storage.log.LogManager.open(LogManager.java:123)
	at com.twitter.aurora.scheduler.storage.log.LogStorage.prepare(LogStorage.java:287)
	... 7 more
Caused by: com.twitter.aurora.codec.ThriftBinaryCodec$CodingException: Failed to deserialize thrift object.
	at com.twitter.aurora.codec.ThriftBinaryCodec.decodeNonNull(ThriftBinaryCodec.java:86)
	at com.twitter.aurora.codec.ThriftBinaryCodec.decode(ThriftBinaryCodec.java:59)
	at com.twitter.aurora.scheduler.log.testing.FileLog.open(FileLog.java:67)
	... 9 more
Caused by: org.apache.thrift.transport.TTransportException: Cannot read. Remote side has closed. Tried to read 1 bytes, but only got 0 bytes. (This is often indicative of an internal error on the server side. Please check your server logs.)
	at org.apache.thrift.transport.TTransport.readAll(TTransport.java:86)
	at org.apache.thrift.protocol.TBinaryProtocol.readAll(TBinaryProtocol.java:362)
	at org.apache.thrift.protocol.TBinaryProtocol.readByte(TBinaryProtocol.java:251)
	at org.apache.thrift.protocol.TBinaryProtocol.readFieldBegin(TBinaryProtocol.java:215)
	at com.twitter.aurora.gen.test.FileLogContents$FileLogContentsStandardScheme.read(FileLogContents.java:349)
	at com.twitter.aurora.gen.test.FileLogContents$FileLogContentsStandardScheme.read(FileLogContents.java:342)
	at com.twitter.aurora.gen.test.FileLogContents.read(FileLogContents.java:292)
	at org.apache.thrift.TDeserializer.deserialize(TDeserializer.java:69)
	at com.twitter.aurora.codec.ThriftBinaryCodec.decodeNonNull(ThriftBinaryCodec.java:79)
	... 11 more

I1213 22:58:27.001 THREAD11 org.apache.zookeeper.server.SessionTrackerImpl.run: SessionTrackerImpl exited loop!
UnresettableLogManager is ignoring a reset() request.
I1213 22:58:27.002 THREAD14 com.twitter.common.application.ShutdownRegistry$ShutdownRegistryImpl.execute: Action controller has already completed, subsequent calls ignored.

After the fix: No exception.

Reviewed at https://reviews.apache.org/r/16261/