pkg/debian: Fix versioning if upstream is dev/rc

An improvement/addition to pull request #658. The version number for logstash changed and it added .dev to the end of the version number. This commit ensures that the debian packages have a clean upgrade path from dev to rc to final.

   * Change the upstream version from 'x.x.x.dev' and 'x.x.x.rcx' to 'x.x.x~dev' and 'x.x.x~rcx'
   * Use UTC instead of local time in the debian version