Adding target-path parameter

[Evengard]

For now, it seems that when diskrsync connects to the target host, it tries to call diskrsync with the same argv[0] it had been called locally. If diskrsync was called just like diskrsync, it issues diskrsync on the target as well, when it is called as /somepath/diskrsync - it executes /somepath/diskrsync on the target too.

It would be nice to override this behaviour, by allowing to set explicitely the target binary path via an option, eg diskrsync --target-path /somepath/diskrsync.