SlapObject: long methods cleanup

extracted methods download_binary_cache(), update_binary_cache(),
_pre_destroy()
SlapObject: removed useless try..finally blocks
SlapObject: cleaner buildout_cfg creation
SlapObject: cleaner handling of sr_symlink
SlapObject: removed method getSupervisorRPC
grid: logger usage % -> ,
SlapObject: removed redundant os.path.exists()
format: some logger syntax, levels and messages