'influxd backup' should create backup directory

[zstyblik]

Hello,

it was somewhat surprising to find out that influx backup expects directory and not a filename. Actually, docs say `` Once you have your snapshot file''. Ok. Clearly, snapshot is created in given directory.

However, the following shouldn't either happen or be handled in better way, resp. check whether directory exists.

root@builder:~# influxd backup -host localhost:8086 /tmp/bar
2016/01/13 17:20:44 influxdb backup
2016/01/13 17:20:44 backing up metastore to /tmp/bar/meta.00
backup: open temp file: open /tmp/bar/meta.00.pending: no such file or directory

Thanks.