Added local port forwarding feature
Changed to establish session and do operation for each session
Added single gateway support
Added multiple gateways support
Extract establishing a session into the session manager
Establish all sessions before calling each operation
Remove local port forwarding feature

This reverts commit 5a3f7f067197108128bb32c499bba7cd8bbc1adf.

Conflicts:
	src/test/groovy/org/hidetake/gradle/ssh/server/PortForwardingSpec.groovy
Add a test for gateway support
Add support for gateways #22

Conflicts:
	src/main/groovy/org/hidetake/gradle/ssh/internal/DefaultSshService.groovy