Cperello/disable ftp chroot option

Zentyal 3.4 ships a vsftp package that works again with the users chroot option so we are able to enable it again. I added anste tests to confirm it:

	Zentyal FTP tests
		ConfigNetSetExternal: OK
		InstallFTP: OK
		EnableModules: OK
		AddUser: OK
		ConfigFTPNonSSLNonAnonymous: OK
		TestPut: OK
		TestGet: OK
		TestPwd: OK
		ConfigFTPNonSSLAnonymousReadWrite: OK
		TestPutAnonymous: OK
		TestGetAnonymous: OK
		ConfigFTPNonSSLAnonymousReadOnly: OK
		TestPutAnonymousReadOnly: OK
		TestGetAnonymousReadOnly: OK
		ConfigFTPNonSSLNonAnonymousWithChroot: OK
		TestPut: OK
		TestGet: OK
		TestPwd: OK
		check-zentyal-log: OK
		check-syslog-apparmor: OK