kpatch: improve "unload --all" error message

In the case of "kpatch unload --all", just show the usage help instead
of this:

  # kpatch unload --all
  basename: unrecognized option '--all'
  Try 'basename --help' for more information.
  unloading patch module:
  basename: unrecognized option '--all'
  Try 'basename --help' for more information.
  rmmod: ERROR: Module  is builtin.
  kpatch: failed to unload patch --all
kpatch: consistent naming: module vs patch

Try to be more consistent with the naming of patch modules.  They are
patch modules, where patch is the adjective and module is the noun.  So
calling them patches is confusing.
Merge pull request #231 from jpoimboe/unload-all-error

kpatch: a few minor script cleanups
improve kpatch unload checking

Currently, kpatch unload passes the raw argument to basename since the
user may pass a path into the subcommand. This makes the argument hard
to validate.  This can be improved since the set of acceptable inputs is
already known, namely the list of loaded patch modules.

This commit changes the kpatch unload subcommand to accept only the
module name, since kpatch should already be aware of it since it is
loaded.  It is then trivial to validate the user input since, if it is
not the name of a loaded module, it is invalid.

Signed-off-by: Seth Jennings <sjenning@redhat.com>