KNOX-2950 - Handling application path aliases

[smolnar82]

What changes were proposed in this pull request?

With this change, our end-users have a way to define custom application path aliases next to the ones we have OOTB to reach certain apps, UIs.
I added the following gateway-site.xml property(ies) to support this feature:

    <property>
        <name>gateway.application.path.alias.$original-application-path-to-match</name>
        <value>$comma-separated-list-of-alias-names</value>
    </property>

where

• $original-application-path-to-match indicates the existing application path we would like to have an alias for
• $comma-separated-list-of-alias-names marks the list of alias names to register (pointing to the same application as the original path above), separated by a comma if there are more

For instance:

    <property>
        <name>gateway.application.path.alias.token-generation</name>
        <value>tokengen</value>
    </property>

will allow end-users to reach the Token Generation UI on both .../token-generation/index.html and .../tokengen/index.html.

How was this patch tested?

Updated JUnit tests and conducted manual testing:

1. Added the following application path aliases in gateway-site.xml (under the existing token-generation/tokengen entry):

    <property>
        <name>gateway.application.path.alias.token-management</name>
        <value>tokenman</value>
    </property>

    <property>
        <name>gateway.application.path.alias.home</name>
        <value>knoxhome, knox-home</value>
    </property>

2. Validated that the Token Generation page is reachable on both paths:

3. Validated that the Token Management page is reachable on both paths:

4. Validated that the Knox Home page is reachable on the original path (/home) as well as on the two path aliases: