secdrivers: Rename @stdin_path argument of virSecurityDomainSetAllLabel()

secdrivers: Rename @stdin_path argument of virSecurityDomainSetAllLabel()

The argument (if not NULL) points to the file the domain is
restoring from. On QEMU command line this used to be '-incoming
$path', but we've switched to passing FD ages ago and thus this
argument is used only in AppArmor (which loads the profile on
domain start). Anyway, the argument does not refer to stdin,
rename it to 'incomingPath' then.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Erik Skultety <eskultet@redhat.com>