virCommandSetDryRun: Add flags to linebreak and strip prefix from the command buffer

virCommandSetDryRun: Add flags to linebreak and strip prefix from the command buffer

virCommandToStringFull used internally when virCommandSetDryRun is
requested allows to strip command path and wrap lines nicely. Expose
these via virCommandSetDryRun so that tests can use those features
instead of local hacks.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>