allow fedora-storage-init to detect encrypted PVs

After unlocking an encrypted volume, let LVM detect a possible PV on it.
This way fedora-storage-init-late.service will be able to activate the VG.

This is a non-upstream patch and it is only temporary until lvm2 is updated
to use udev and to get rid of /etc/lvm/cache. According to Milan Bro┼ż it is
already implemented upstream.

https://bugzilla.redhat.com/show_bug.cgi?id=708684

Index: systemd-26/src/cryptsetup-generator.c
===================================================================
--- systemd-26.orig/src/cryptsetup-generator.c
+++ systemd-26/src/cryptsetup-generator.c
@@ -131,8 +131,10 @@ static int create_disk(
                 "RemainAfterExit=yes\n"
                 "TimeoutSec=0\n" /* the binary handles timeouts anyway */
                 "ExecStart=" SYSTEMD_CRYPTSETUP_PATH " attach '%s' '%s' '%s' '%s'\n"
+                "ExecStart=-/sbin/pvs -o pv_uuid '/dev/mapper/%s'\n"
                 "ExecStop=" SYSTEMD_CRYPTSETUP_PATH " detach '%s'\n",
                 name, u, strempty(password), strempty(options),
+                name,
                 name);
 
         if (has_option(options, "tmp"))