Fix: libcrmcommon: Restore getopt behavior in stonith_admin.

This patch introduces a new pcmk__cmdline_preproc function which
restores getopt's single character argument behavior that was lost when
switching to glib. getopt recognizes a string like "-xval" to be the -x
command line option with a value of val. glib would recognize that as
the four command line options -x, -v, -a, and -l.

Passing the command line through this new function converts it into
something that glib understands. See the documentation and comments on
this function for more details.