Refactor: libcrmcommon: pcmkoutput_t in pcmkxml_show() in patchset.c

These are the minimum modifications required to enable functions within
patchset.c to call pcmkxml_show() with a pcmkoutput_t argument.

For now, pcmk__xml_log_patchset() creates a new output object, passes it
to the appropriate v1/v2 function, and frees it before returning. Soon a
message function-based implementation will replace this.

Change some function names to use "show" instead of "log" since the
output object may be a text object. Not really important since we'll use
message functions soon.

We temporarily have to check the output type in xml_show_patchset_v1()
to keep the code simple and continue setting the diff_short option
appropriately. That too will go away when we use message functions.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>