Description of problem:
plymouthd executed with the "--debug --debug-file=/tmp/plymouth_debug" options doesn't save debug messages to the specified file.

[root@localhost ~]# rpm -q plymouth
plymouth-0.8.9-0.24.20140113.el7.x86_64
[root@localhost ~]# plymouthd --debug --debug-file=/tmp/plymouth_debug
[main.c:2084]                        initialize_environment:initializing minimal work environment
[main.c:1889]                       get_kernel_command_line:opening /proc/cmdline
[main.c:1898]                       get_kernel_command_line:reading kernel command line
[main.c:1919]                       get_kernel_command_line:Kernel command line is: 'BOOT_IMAGE=/vmlinuz-3.10.0-327.el7.x86_64 root=/dev/mapper/rhel-root ro crashkernel=auto rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb quiet LANG=en_US.UTF-8
'
[main.c:2103]                        initialize_environment:checking if '/dev/tty1' exists
[main.c:1933]                               check_verbosity:checking if tracing should be enabled
[main.c:2009]                               check_verbosity:tracing shouldn't be enabled!
[main.c:2027]                                 check_logging:checking if console messages should be redirected and logged
[main.c:2036]                                 check_logging:logging will be enabled!
[main.c:2117]                        initialize_environment:source built on Oct 26 2015
[root@localhost ~]# ls -l /tmp/plymouth_debug
ls: cannot access /tmp/plymouth_debug: No such file or directory
[root@localhost ~]#

Version-Release number of selected component (if applicable):
plymouth-0.8.9-0.24.20140113.el7

How reproducible:
always

Steps to Reproduce:
1. plymouthd --debug --debug-file=/tmp/plymouth_debug
2. less /tmp/plymouth_debug

Actual results:
/tmp/plymouth_debug doesn't exist

Expected results:
/tmp/plymouth_debug with debug messages exists