Mount the entire user SSH directory into build container

This enables the user to use an key file format (RSA, ED25519, ...).
Additionally, it allows more complex workflows (such as different SSH keys for
specfic sites, such as Github or Bitbucket), since the .ssh/config
file is also mounted into the container.

Fixes serverless#488

Author: jacksgt

lib/pip.js

@@ -201,10 +201,7 @@ function installRequirements(targetFolder, serverless, options) {
     if (options.dockerSsh) {
       // Mount necessary ssh files to work with private repos
       dockerCmd.push(
-        '-v',
-        `${process.env.HOME}/.ssh/id_rsa:/root/.ssh/id_rsa:z`,
-        '-v',
-        `${process.env.HOME}/.ssh/known_hosts:/root/.ssh/known_hosts:z`,
+        `${process.env.HOME}/.ssh/:/root/.ssh/:z`,
         '-v',
         `${process.env.SSH_AUTH_SOCK}:/tmp/ssh_sock:z`,
         '-e',