CC - Fix slow JaCoCo Sensor when analyzing large .exec files.

Summary:
JaCoCo Sensor is slow when analyzing large .exec files.

Analysis:
1. Replace JaCoCo binary output in 
\sonar-java\sonar-jacoco-plugin\src\test\resources\org\sonar\plugins\jacoco\JaCoCoSensorTest\jacoco.exec with an large file (eg. 60MB).
2. Run org.sonar.plugins.jacoco.JaCoCoSensorTest
- Baseline: 100s
3. Using a profiler, the biggest portion time was spent in AbstractAnalyzer.readExecutionData(); which calls ExecutionDataReader.read().
(https://github.com/SonarSource/sonar-java/blob/7f5a848a37b84bb8fc2c413aea3a02edbd932d15/sonar-jacoco-plugin/src/main/java/org/sonar/plugins/jacoco/AbstractAnalyzer.java#L122-L135)
4. ExecutionDataReader calls InputStream.readByte() in a loop. Which can take a long time for a large file.
(https://github.com/jacoco/jacoco/blob/283abfa148b749678924b5e75eabd35a2d58f9f8/org.jacoco.core/src/org/jacoco/core/data/ExecutionDataReader.java#L78-L92)

Since AbstractAnalyzer instantiates an ExecutionDataReader and pass in a FileInputStream, each call to read byte(s) will necessitate an file system I/O call. Using a BufferInputStream should should the performance.

Test:
Run JaCoCoSensorTest
- Baseline (unbuffered):          100s
- BufferedInputStream (default):   30s
- BufferedInputStream (8K):        30s
- BufferedInputStream (16K):       28s
- BufferedInputStream (32K):       28s