Set compression flag for SSH session.

Now, compression flag of SSH is dependent on the user configuration such as ssh_config.
It may take some time to transfer the file.


Example: About 100MB file transfer.

```
# case compression=true
real	0m16.905s
user	0m7.740s
sys	0m0.505s

# case compression=false
real	0m46.755s
user	0m3.001s
sys	0m0.401s
```