Remove customized require behaviors and modify the bin executable
to check for missing tools that Vagrant expects to exist when
running outside of an installer.
This ensures that rsync can be installed on an Alpine Linux machine where the
apk cache may not be current.
Display a warning if the vagrant-alpine plugin is installed, since Alpine guest
support has been merged into Vagrant core.
The workaround for the broken repository should be safe to be removed,
since the last affected Alpine version (<=3.3) EOL'd in November of 2017.
The remaining important commands can be split out into seperate calls
of sudo(), which removes the need for manual exit-code checking
(since it aborts by itself when a command fails) and makes the code
easier to handle in general.
