Adding SCP option

To get around problems with file_write failing on large files, using
SCP : requires host and user to have been initialised
Fix if the host has a port suffix

Port suffix doesn't work with hostname - this is common for Vagrant
installations and so remove the port - this can be specified in the
ssh_config file
Merge pull request #135 from uwacsp/dglance-file_scp

Adding SCP option to file_write, file_ensure and file_upload