Set Synchrony Java temp directory by default to be Confluence temp directory.

During the startup of Confluence application Synchrony Java on Linux will use /tmp for executing some libraries. Example for that can be this KB https://confluence.atlassian.com/confkb/editor-fails-to-load-in-confluence-6-x-due-to-could-not-initialize-class-org-xerial-snappy-snappy-error-859462192.html.

By defining something like java.io.tmpdir=<confluence-home>/tmp/ in synchrony startup parameters we could avoid potential problems where /tmp does not have right attributes and also all of Confluence processes will be stored only in <confluence-home> and <confluence-install> directories.