Correct parsing error

While processing the pre/post install/uninstall scripts, in the case of
a one-line script of the form "%post -n <package_name> -p <command>",
if the package name or the command contains "-p" or "-n", parsing is
wrong. Usig " -p " and " -n " corrects this error in our cases. The
only package found with this error is pkmgr-info-parser. If a command
would happen to have a "-p" or "-n" option, parsing would fail, even
with this patch. Another solution would need to be found.

Signed-off-by: Kévin THIERRY <kevin.thierry@open.eurogiciel.org>