lx speed-test
skip files with length < 1M
refine speed-test output
remove duplicate vod nodes from list so I can priority some nodes easily
move shared code to lixian_nodes
use --node=fastest to detect fastest node automatically
make sure the default node is in the candidates
lx download --node=fast --node-detection-acceptable=1M
if no acceptable node is detected, use the fastest node
encode dirname safely