50plymouth/plymouth-pretrigger.sh: respect primary console setting

The kernel's primary console device is determined by the last "console="
argument on the kernel command line. This setting should be respected by
dracut-generated initial RAM disks.

Steps to Reproduce:
(Easiest using a KVM VM, virt-manager and "virsh console")
1. Boot with a kernel command line ending in
 console=tty0 console=ttyS0,115200
2. Observe both tty0 and ttyS0.

The output of init scripts is sent to ttyS0, as the final "console="
argument determines the primary console device as per
Documentation/serial-console.txt in the kernel sources.

https://bugzilla.redhat.com/show_bug.cgi?id=752073

modules.d/50plymouth/plymouth-pretrigger.sh

@@ -18,7 +18,9 @@ if getargbool 1 plymouth.enable && getargbool 1 rd.plymouth -n rd_NO_PLYMOUTH; t
 
     info "Starting plymouth daemon"
     mkdir -m 0755 /run/plymouth
-    [ -x /lib/udev/console_init ] && /lib/udev/console_init /dev/tty0
+    consoledev=$(getarg console= | sed -e 's/,.*//')
+    consoledev=${consoledev:-tty0}
+    [ -x /lib/udev/console_init ] && /lib/udev/console_init "/dev/$consoledev"
     [ -x /bin/plymouthd ] && /bin/plymouthd --attach-to-session --pid-file /run/plymouth/pid
     /bin/plymouth --show-splash 2>&1 | vinfo
     # reset tty after plymouth messed with it