Support independent building of modules

According to the comments, this issue aims to change all modules.
--------------

Currently, there exist minor build errors when we build Tang and Wake module directly in their folders. These errors are related to just `findbugs` plug-in, not REEF components.

$ mvn clean install
INFO] ------------------------------------------------------------------------
[ERROR] Could not find resource '/Users/dongjoon/reef/lang/java/reef-wake/lang/java/reef-common/src/main/resources/findbugs-exclude.xml'. -> [Help 1]
[ERROR] 

By overriding rootPath property in their pom files, we can build Tang and Wake modules independently again.

+    <properties>
+        <rootPath>${basedir}/../../../..</rootPath>
+    </properties>