What is this PR for?

Improving logging information on error

What type of PR is it?

Fix/Improvement

Todos

• - fix logging

Is there a relevant Jira issue?

May not require issue

How should this be tested?

Can be tested with any error for storage initialization
For example:

1. in conf/zeppelin-env.sh add the following line
   export ZEPPELIN_NOTEBOOK_STORAGE="org.apache.zeppelin.notebook.repo.VFSNotebookRepo,org.apache.zeppelin.notebook.repo.DummyNotebookRepo"
2. Start Zeppelin
3. Previously you would see one line warning, now you would see more detailed trace-back as well.

Screenshots (if appropriate)

Before:

Failed to initialize com.nflabs.zeppelinhub.notebook.repo.DummyNotebookRepo notebook storage class java.lang.reflect.InvocationTargetException

After:

WARN [2016-01-13 22:43:05,557] ({main} NotebookRepoSync.java[<init>]:81) - Failed to initialize com.nflabs.zeppelinhub.notebook.repo.DummyNotebookRepo notebook storage class
java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)

Questions:

• Does the licenses files need update? No
• Is there breaking changes for older versions? No
• Does this needs documentation? No