[ZEPPELIN-6181] fix can't login with plus char as password

[sh1nj1]

What is this PR for?

This PR fixes an issue where usernames or passwords containing a "+" character were being incorrectly converted to a " "(space), preventing users from signing in with password containing "+" character

What type of PR is it?

Bug Fix

Todos

What is the Jira issue?

• https://issues.apache.org/jira/browse/ZEPPELIN-6181

How should this be tested?

• Add account using password containing "+" character in shiro.ini
• Test if it can do login successfully

Screenshots (if appropriate)

Questions:

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