client: Refactored Vivaldi thread.

- Resolving of an OSD's UUID is handled by the ExecuteSyncRequest call now.

- The main goal of the refactoring was to realize a non-leaking, non-blocking interruption of the Vivaldi thread. This was tested with the following two commands which executed always a new instance of Valgrind running mount.xtreemfs and unmounted the client after random time:

while true; do vgcheck ./mount.xtreemfs demo.xtreemfs.org/demo ~/mnt -f --vivaldi-enable -d DEBUG --vivaldi-recalculation-interval 0 --vivaldi-recalculation-epsilon 0 --vivaldi-max-iterations-before-updating 1 --vivaldi-enable-dir-updates --request-timeout 5; done

while true; do wait=$(echo $RANDOM | awk 'END { print ($1 / 2048) }'); echo "waiting $wait seconds"; sleep $wait; fusermount -u ~/mnt; done

whereas vgcheck is an alias for: valgrind --gen-suppressions=yes --leak-check=full --show-reachable=yes --vgdb=yes 

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@3047 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534