[CHEF-5269] Added additional ruby environment files to .gitignore.

- .ruby-version
- .ruby-gemset
Change chef-full bootstrap template to install the current latest version of the workstation version to resolve errors while bootstrapping with a pre-release version.
require chef/mixin/command in Knife::Ssh to solve below error:

bundle exec knife bootstrap 127.0.0.1
Connecting to 127.0.0.1
ERROR: knife encountered an unexpected error
This may be a bug in the 'bootstrap' knife command or plugin
Please collect the output of this command with the `-VV` option before filing a bug report.
Exception: NameError: uninitialized constant Chef::Mixin::Command
Merge pull request #1403 from alex-ethier/CHEF-5269

[CHEF-5269] Added additional ruby environment files to .gitignore.
Changelog info for CHEF_4911.
Merge pull request #1420 from opscode/sersut/CHEF-4911

Give -p option to install.sh if we are bootstrapping a pre-release version