Generic MXBean Utility class to support all JDK vendors

This issue is related to JIRA https://issues.apache.org/jira/browse/HBASE-6945. This issue is opened to propose the use of a newly created generic org.apache.hadoop.hbase.util.OSMXBean class that can be used by other classes. JIRA HBASE-6945 contains a patch for the class org.apache.hadoop.hbase.ResourceChecker that uses OSMXBean. With the inclusion of this new class, HBase can be built and become functional with JDKs and JREs other than what is provided by Oracle.

This class uses reflection to determine the JVM vendor (Sun, IBM) and the platform (Linux or Windows), and contains other methods that return the OS properties - 1. Number of Open File descriptors; 2. Maximum number of File Descriptors.

This class compiles without any problems with IBM JDK 7, OpenJDK 6 as well as Oracle JDK 6. Junit tests (runDevTests category) completed without any failures or errors when tested on all the three JDKs.The builds and tests were attempted on branch hbase-0.94 Revision 1396305.