[HOTFIX] fix: DON'T run npm clean in maven clean phase (CI related, Build failure in web)

[1ambda]

What is this PR for?

maven clean executes npm run clean after #1824. but running npm commands requires installing, it's impossible to clean before installing it.

This PR resolve CI break (see broken RAT build profiles)

• https://travis-ci.org/apache/zeppelin/builds/188895921
• https://travis-ci.org/apache/zeppelin/builds/188782988

What type of PR is it?

[Bug Fix | Hot Fix]

Todos

Nothing

What is the Jira issue?

ZEPPELIN-1850

How should this be tested?

The first build profile (RAT) should pass CI.

Screenshots (if appropriate)

[INFO] --- frontend-maven-plugin:1.3:npm (npm clean) @ zeppelin-web ---
...
[INFO] Running 'npm run clean' in /Users/lambda/github/apache-zeppelin/zeppelin-bug/zeppelin-web
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 0.701 s
[INFO] Finished at: 2017-01-05T03:55:32+09:00
[INFO] Final Memory: 21M/982M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal com.github.eirslett:frontend-maven-plugin:1.3:npm (npm clean) on project zeppelin-web: Failed to run task: 'npm run clean' failed. java.io.IOException: Cannot run program"/Users/lambda/github/apache-zeppelin/zeppelin-bug/zeppelin-web/node/node" (in directory "/Users/lambda/github/apache-zeppelin/zeppelin-bug/zeppelin-web"): error=2, No such file or directory -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal com.github.eirslett:frontend-maven-plugin:1.3:npm (npm clean) on project zeppelin-web: Failed to run task
...
 
[ERROR]
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException

Questions:

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

[Leemoonsoo]

LGTM. It fixes CI build failure. Merge to master as a hotfix