fix #371: lx delete --failed
minor change
fix #374: add verificiation code when adding a batch of tasks
lx config verification-code-path ...
add verification code when adding bt task
Catch possible exception for os.makedirs.
Don't throw exception when dir exists.
Merge pull request #379 from leojay/master

Catch possible exception for os.makedirs.
update verification code
Merge branch 'master' of github.com:iambus/xunlei-lixian
Mergred latest changes from iambus
Merge branch 'master' of https://github.com/iambus/xunlei-lixian