re-apply changes from #91 for a clean commit history
remove `#quiet_system` as it is dead code by now
Rename ssh identity file option

In order to match the options from knife bootstrap and avoid
option namespace problems.  The old --ssh-identity option is
kept but deprecated in favor of the new --identity-file option.
If both options are specified the new option takes precedence
over the older deprecated option.
Deprecation message for `--ssh-identity` tells user the new option

Also added ui warning message if `--ssh-identity` is used.
Rename validate_first_cli_arg_is_a_hostname to validate_ssh_options
Move handling of the --ssh-identity to #validate_ssh_options!
Merge branch 'rename_ssh_option'

Fixes #178. Thanks to @russellcardullo.
Call #validate_ssh_options! in ssh tests
Add --ssh-user option
Merge pull request #156 from tknerr/windows-compat

Windows Client Compatibility - Take 2 with Clean Commit History
Merge pull request #179 from tmatilai/ssh-user

Support `--ssh-user` option
Upgrade dev gems