Improve the usage of Sysfs in the interaction with EV3Dev #765

In the previous Issue:
#748

We improved the performance with current architecture, the usage of Sysfs. Sysfs in the current form, is a stateless class with static methods.

Ideas to improve in this iteration:

• Moving from static methods, to instance methods
• Add setSysfs to Mock Sysfs to improve testing. Using Guava, it could be possible to expose only for testing with the annotation @VisibleForTesting but I don´t want to increase the weight of the jar in 2mb.

@dwalend, what other ideas, do you have?
@JakubVanek, what other ideas, do you have?

In your opinion, what state is necessary to maintain in Sysfs and have some kind of concurrency protection?

Criterias for PR:

• Branch: sysfs_perf2
• Code pass Checkstyle: gradle checkstyleMain
• Benchmarks: JMH
• Complexity: Reduced
• Number of changes: Minimum
• Tests: Every new class, requiere Unit Tests. Review how to add Concurrency tests to avoid concurrency issues.

We will analyse for the classes:

• ev3dev.sensors.Battery;
• ev3dev.actuators.ev3.EV3Led;
• ev3dev.actuators.lego.motors.EV3LargeRegulatedMotor;

We will begin with Battery, an easy case and later, we will tackle a complex case like a Motor.

Juan Antonio