time-machine: Honor the standard build options.

time-machine: Honor the standard build options.

* guix/scripts/time-machine.scm (show-help): Call 'show-build-options-help'.
(%options): Add %STANDARD-BUILD-OPTIONS.
(%default-options): New variable.
(parse-args): Pass (list %default-options) to 'parse-command-line' and
remove #:build-options? parameter.
(guix-time-machine): Call 'set-build-options-from-command-line' and wrap
'cached-channel-instance' call in 'with-status-verbosity'.
* doc/guix.texi (Invoking guix time-machine): Mention common build options.