TAJO-1909: Eliminate remained explicit diamond expressions

[dkhwangbo]

I found some remain part after working TAJO-1844.
This is another work of removing it.

[dkhwangbo]

Travis-ci gives me the error message but This commit pass the same test in my local environment.

[hyunsik]

That's not your fault. I'll manually verify the patch and review it.

[hyunsik]

Could you rebase the patch? The patch causes the following error:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.3:compile (default-compile) on project tajo-common: Compilation failure
[ERROR] /home/hyunsik/Code/tajo/tajo/tajo-common/src/main/java/org/apache/tajo/util/ShutdownHookManager.java:[103,34] incompatible types: java.util.Set<java.lang.Object> cannot be converted to java.util.Set<org.apache.tajo.util.ShutdownHookManager.HookEntry>

#778 changes the source and target JVM of tajo-common to 1.7. It may cause this problem, I think.

[dkhwangbo]

@hyunsik Thanks for your reply. I rebase it. Please review again.