LocalLargeFileRepository#getContentPath: Avoid String concatentation

The CONTENT_PATH constant is not used ouside the class since
change I4339d714f. Make it private.

Also rename it to CONSTANT_PATH_TEMPLATE and use String.format to
generate the content path from the backend name.

Change-Id: If12d8f3c6350155d867f1b52ff040b2f00e89119
1 file changed