Race-condition on DeployDynamoDBLocal in multi-subproject builds

[rtyley]

We've been using the 'different port for each subproject' strategy described in #53, but have noticed that there's a race-condition on the deploy-dynamodb-local task.

• With sbt running subproject A & B simultaneously, both threads see there is no dynamodb-local folder in the root of the project, and start downloading the tar file from S3
• Project A completes the download first, and begins extracting all files from the archive...
• Project B completes the download second- at this point it may briefly corrupt or delete the file that Project A has downloaded before replacing it with an identical copy.
• Project A is now extracting files from a corrupt archive, and racing with B to extract all the correct files to the folder
• Typically, the DynamoDBLocal_lib folder ends up containing only a subset of the required jar files, possibly with a jar corrupted as well.
• When the DynamoDBLocal server runs, it will typically give a java.lang.ClassNotFoundException, and then never ever successfully start, resulting in behaviour like that seen in Startup process hangs infinitely #50

Port:   8043
InMemory:       true
DbPath: null
SharedDb:       false
shouldDelayTransientStatuses:odbfalse 0s
CorsParams:lab /*Test / executeTests 1s
  | => sharedLib / startDynamodbLocal 3s
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/logging/log4j/spi/ExtendedLogger
	at com.amazonaws.services.dynamodbv2.local.shared.logging.LogManager.<clinit>(LogManager.java:28)
	at com.amazonaws.services.dynamodbv2.local.server.DynamoDBProxyServer.<clinit>(DynamoDBProxyServer.java:36)
	at com.amazonaws.services.dynamodbv2.local.main.ServerRunner.createServer(ServerRunner.java:120)
	at com.amazonaws.services.dynamodbv2.local.main.ServerRunner.createServerFromCommandLineArgs(ServerRunner.java:116)
	at com.amazonaws.services.dynamodbv2.local.main.ServerRunner.main(ServerRunner.java:71)
Caused by: java.lang.ClassNotFoundException: org.apache.logging.log4j.spi.ExtendedLogger
	at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
	... 5 more

It's a particular stumbling block for new-starters on our team as it the first thing they encounter when they're trying to run our tests!

I guess fix for this would probably involve downloading & extracting the resources to a temporary location before doing a quick move of the dynamodb-local folder into the right place.