Remove Maven dependency to run apps in ITs and stop process leaks.

Integration tests invoke `dapr run` with a `mvn` command. Instead, change how services are invoked for ITs.

### 1. Use `daprd` instead of `dapr`
Follow instructions in [debugging with daprd in IntelliJ](https://github.com/dapr/docs/tree/master/howto/intellij-debugging-daprd) to understand how `daprd` can be invoked directly. Change [DaprRun.java](https://github.com/dapr/java-sdk/blob/master/sdk-tests/src/test/java/io/dapr/it/DaprRun.java) to invoke daprd in a separate process.

### 2. Run test app as a new thread in same JVM as tests
Now, instead of running the service application as a process by invoking `mvn`, run the main function directly as a new thread inside the same JVM as tests. This will avoid having to build a separate fatjar only for test apps. There are environment variables expected by the test app, and those cannot be changed at runtime. On the other hand, all environment variables defined in [Properties.java](https://github.com/dapr/java-sdk/blob/master/sdk/src/main/java/io/dapr/utils/Properties.java) can be overridden via System properties. Since System Properties are global, see this [work around](https://stackoverflow.com/questions/9579958/system-setproperty-used-by-a-thread-impacts-other-thread-in-communication-to-ext) on how to have System Properties in ThreadLocal (not ideal for production but OK for tests IMO).

### 3. Make test app optional in `DaprRun.java`
Some tests do not need a test app, they just need `daprd`. So, offer a new constructor in `DaprRun.java` that does not have a test app class. Remove [EmptyService.java](https://github.com/dapr/java-sdk/blob/master/sdk-tests/src/test/java/io/dapr/it/services/EmptyService.java) and use the new constructor for all previous uses of that class.

### 4. Stopping `daprd`
Make sure that `DaprRun.java` stops `daprd` in `stop()` method - try gracefully for 1 minute and then forcefully. Because we are not using `dapr` anymore, `dapr stop` will not work anymore. Stop the process from JVM directly.

### 5. Verify process leaks.
* Run ITs once and use Sysinternals' `pskill.exe` as `pskill daprd.exe` and validate no process was killed. For unix systems, use `ps auxwww | grep daprd` and validate there is no `daprd` process in the output, only the `grep` process. Feel free to use another solution to validate this if preferred.
* Artificially make one of the ITs fail an assertion and run ITs. Replay validation for no `daprd` process leaked.
* Artificially throw an exception in the `@Before` method of an IT and run ITs. Replay validation for no `daprd` process leaked.