Oh.. I didn't notice this before.
According to
http://subversion.1072662.n5.nabble.com/Help-with-SVNKit-use-on-AWS-machines-td3539.html,
it seems basic behavior of svnkit and I need to fix code to not use ".subversion folder"
Is it difficult for you to provide write permission on /c9/home/userName/.subversion/ folder?
Otherwise please try to provide -Duser.home=/c9/apps/ngrinder_home in the JAVA_OPTS as well.
I'm not exactly sure it's working or not but worth to try.