Introduce go.crypto/ssh support

Introduce go.crypto/ssh support

A new "client key directory" is introduced,
which may contain one or more SSH key pairs.
The client key directory is initialised to
$JUJU_HOME/ssh in juju/conn.go. If the
directory does not exist, it is created with
a new 2048-bit RSA keypair.

If the default SSH client is not available
at bootstrap time, then a go.crypto/ssh client
will be used; this client will attempt to use
each of the key pairs it finds in the client
key directory.

The OpenSSH client (in utils/ssh/ssh_openssh.go)
is modified to use any of the default SSH
identities, or any of the ones found in the
client key directory.

Fixes #1263851

https://code.launchpad.net/~axwalk/juju-core/ssh-gocrypto-client/+merge/200628

(do not edit description out of merge proposal)

[axw, 2014-01-07 06:38:02]

Please take a look.

[axw, 2014-01-10 03:33:04]

On 2014/01/07 06:38:02, axw wrote:
> Please take a look.

I'm going to split this up, it's rather large. I would appreciate comments on
direction, though.

[thumper, 2014-01-10 03:59:23]

I think the general approach is good, but there will be issues with the identity
file that my branch has introduced.

https://codereview.appspot.com/48370043/diff/1/cloudinit/sshinit/configure.go
File cloudinit/sshinit/configure.go (right):

https://codereview.appspot.com/48370043/diff/1/cloudinit/sshinit/configure.go...
cloudinit/sshinit/configure.go:54: cmd.Stdin = strings.NewReader(script)
One thing I noticed was the need for a carriage return on the end.
Does the script end with a new line?

https://codereview.appspot.com/48370043/diff/1/environs/config/authkeys.go
File environs/config/authkeys.go (right):

https://codereview.appspot.com/48370043/diff/1/environs/config/authkeys.go#ne...
environs/config/authkeys.go:40: var err error
Wondering if this function should perhaps be moved into utils/ssh?

https://codereview.appspot.com/48370043/diff/1/environs/manual/fakessh.go
File environs/manual/fakessh.go (right):

https://codereview.appspot.com/48370043/diff/1/environs/manual/fakessh.go#new...
environs/manual/fakessh.go:33: head >/dev/null
Given the number of different places we mock out the ssh executable, wondering
if we should have some standard place for things like this, perhaps
"testing/ssh" ?

https://codereview.appspot.com/48370043/diff/1/environs/sshstorage/storage.go
File environs/sshstorage/storage.go (right):

https://codereview.appspot.com/48370043/diff/1/environs/sshstorage/storage.go...
environs/sshstorage/storage.go:48: return ssh.Command(host, []string{"bash",
"-c", command}, &options)
bash or /bin/bash ??

We have both in the codebase, and I think we should be consistent with
ourselves.

Personally I don't care too much which we choose, just that we have one.

https://codereview.appspot.com/48370043/diff/1/utils/ssh/ssh.go
File utils/ssh/ssh.go (right):

https://codereview.appspot.com/48370043/diff/1/utils/ssh/ssh.go#newcode18
utils/ssh/ssh.go:18: passwordAuthDisabled bool
hmm.. one of my branches adds an identity file option using the old way.  This
will need to be taken into account some how.

https://codereview.appspot.com/48370043/diff/1/utils/ssh/ssh_gocrypto.go
File utils/ssh/ssh_gocrypto.go (right):

https://codereview.appspot.com/48370043/diff/1/utils/ssh/ssh_gocrypto.go#newc...
utils/ssh/ssh_gocrypto.go:39: func (c *GoCryptoClient) Command(host string,
command []string, options *Options) *Cmd {
Lots of public functions missing docs.

https://codereview.appspot.com/48370043/diff/1/utils/trivial.go
File utils/trivial.go (right):

https://codereview.appspot.com/48370043/diff/1/utils/trivial.go#newcode66
utils/trivial.go:66: // quotes as necessary; each argument is single-quoted.
this isn't escaping slashes... is it?