[Java] Add static method RocksDB.loadLibrary()

Summary:
Add static method RocksDB.loadLibrary() which loads necessary library
files.

Test Plan:
make rocksdbjava
make jtest
make jdb_bench
java/jdb_bench.sh

Reviewers: haobo, dhruba, sdong, ankgup87, rsumbaly, swapnilghike, zzbennett

Reviewed By: ankgup87

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18375

java/org/rocksdb/util/Environment.java

@@ -0,0 +1,37 @@
+package org.rocksdb.util;
+
+public class Environment {
+  private static String OS = System.getProperty("os.name").toLowerCase();
+
+  public static boolean isWindows() {
+    return (OS.indexOf("win") >= 0);
+  }
+
+  public static boolean isMac() {
+    return (OS.indexOf("mac") >= 0);
+  }
+
+  public static boolean isUnix() {
+    return (OS.indexOf("nix") >= 0 ||
+            OS.indexOf("nux") >= 0 ||
+            OS.indexOf("aix") >= 0);
+  }
+
+  public static String getSharedLibraryName(String name) {
+    if (isUnix()) {
+      return String.format("lib%s.so", name);
+    } else if (isMac()) {
+      return String.format("lib%s.dylib", name);
+    }
+    throw new UnsupportedOperationException();
+  }
+
+  public static String getJniLibraryName(String name) {
+    if (isUnix()) {
+      return String.format("lib%s.so", name);
+    } else if (isMac()) {
+      return String.format("lib%s.jnilib", name);
+    }
+    throw new UnsupportedOperationException();
+  }
+}