RFC: bash integration

[bendikro]

This is more of an request for comments than a ready-to-be-merged PR.

This implements parts of the functionality described in #22 (A command line interface for selecting identity and listing identities and keys).

From the commit message:

Add improved bash support and ssh_ident_cli.py CLI script

* Add setting per-shell ssh identity
  Support changing the active ssh identity by using bash functions
  to set the SSH_IDENT variable for the shell.

* Hostname completion
  Add support for hostname completion with the currently active ssh
  identity by adding a wrapper script for ssh bash completion that
  sets the config as a command line option.

* Add config option to define bash functions that overload
  ssh, scp, sftp, and rsync commands

* Add tox.ini and fix some pep8 warnings

To test with a develop install:

mkdir  ~/ssh-ident-install
export PYTHONPATH=~/ssh-ident-install
python setup.py develop --install-dir=~/ssh-ident-install --symlinks

In .bashrc

SSH_IDENT_INSTALL_PATH="~/ssh-ident-install"
export PATH=$PATH:$SSH_IDENT_INSTALL_PATH
source ${SSH_IDENT_INSTALL_PATH}/ssh_ident.sh

To activate in a shell, execute:

ssh_ident_activate

and the active ssh identity should be displayed in the prompt.

Change identity with:

ssh_ident -s <identity>

List identities:

ssh_ident -l

Deactivate with

ssh_ident_deactivate

Note: The current bash-completion script depends on ssh bash completion to be available at

/usr/share/bash-completion/completions/ssh