Can now generate constant cpu load

Added strategy to generate constant cpu load for a defined duration.
The amount of cpu load to be generated and the duration can be
configured by updating the values in configs/const_cpuload_config.yaml.

Redesign with load generators as strategies

1. Each different load generator now is a LoadGenerationStrategyI. Instantiation uses a simple factory that takes the config file and unmarshals it into the necessary load generator.
2. Added command-line options for specifying the type of load to be generated.
3. Load generation config files are written in YAML format.
4. Using Gradle as the build tool.
5. Dockerfile updated to now build single image for system-load-generator.
6. Image pkaushi1/system-load-generator:v2 created and pushed to docker hub.

Initial release

First release of system load generator. The following types of load can be generated.

1. CPU Load.
2. Load Average.
3. CPU Load with Memory Pressure.

Uncomment the necessary sections in the Dockerfile depending on the type of load to be generated and build the docker image.
You can also use one of the following pre-built docker images.

1. CPU Load - pkaushi1/cpu-load-generator:latest
2. Load Average - pkaushi1/cpu-loadavg-generator:latest
3. CPULoad with Memory Pressure - pkaushi1/cpu-load-with-memory-pressure-generator:latest