Add `vagrant plugin list` command.

This command is useful for seeing what plugins are installed.  For
example, whether the "sahara" plugin is installed and hence, whether
"sandbox" subcommands are available.
Merge branch 'plugin'
Add method to get the vagrant version.

This is equivalent to parsing the version number from the output
of the `vagrant --version` command.
Merge branch 'version'
Add reload command. Update up and provision commands.

Options for --provision-with and --provision were added to the up and
provision commands where needed.

The reload command (similar to the up command) was added.
Bump version.