[CI] increase timeout of website build to 120 mins

Descriptions of the changes in this PR:

*Motivation*

Since we have more releases, the build time for website is increasing to beyond 30 min.
Increase it to 120 mins for now




Reviewers: Enrico Olivelli <eolivelli@gmail.com>, Jia Zhai <None>

This closes apache#1844 from sijie/change_website_buildtime

.test-infra/jenkins/common_job_properties.groovy

@@ -35,7 +35,7 @@ class common_job_properties {
             'https://gitbox.apache.org/repos/asf/bookkeeper.git',
             branch,
             'git-websites',
-            30)
+            120)
   }
 
   // Sets common top-level job properties for main repository jobs.