Description of problem:
The option „-f /var/log/wpa_supplicant.log” appears two time on the commandline of wpa_supplicant. 
It is defined twice. First in /etc/sysconfig/wpa_supplicant and second in /usr/lib/systemd/system/wpa_supplicant.service

Version-Release number of selected component (if applicable):
wpa_supplicant-2.0-17.el7_1.x86_64

How reproducible:
always

Steps to Reproduce:
1. yum install wpa_supplicant
2. systemctl start wpa_supplicant
3. ps -ef | grep [w]pa_supplicant

Actual results:
root      1277     1  0 06:49 ?        00:00:00 /usr/sbin/wpa_supplicant -u -f /var/log/wpa_supplicant.log -c /etc/wpa_supplicant/wpa_supplicant.conf -u -f /var/log/wpa_supplicant.log -P /var/run/wpa_supplicant.pid

Expected results:
root      1277     1  0 06:49 ?        00:00:00 /usr/sbin/wpa_supplicant -u -f /var/log/wpa_supplicant.log -c /etc/wpa_supplicant/wpa_supplicant.conf -P /var/run/wpa_supplicant.pid

Additional info:

$: cat /etc/sysconfig/wpa_supplicant 
# Use the flag "-i" before each of your interfaces, like so:
#  INTERFACES="-ieth1 -iwlan0"
INTERFACES=""

# Use the flag "-D" before each driver, like so:
#  DRIVERS="-Dwext"
DRIVERS=""

# Other arguments
#   -u   Enable the D-Bus interface (required for use with NetworkManager)
#   -f   Log to /var/log/wpa_supplicant.log
#   -P   Write pid file to /var/run/wpa_supplicant.pid 
#        required to return proper codes by init scripts (e.g. double "start" action)
#        -B to daemonize that has to be used together with -P is already in wpa_supplicant.init.d
OTHER_ARGS="-u -f /var/log/wpa_supplicant.log -P /var/run/wpa_supplicant.pid"


---

$: cat /usr/lib/systemd/system/wpa_supplicant.service 
[Unit]
Description=WPA Supplicant daemon
Before=network.target
After=syslog.target

[Service]
Type=dbus
BusName=fi.w1.wpa_supplicant1
EnvironmentFile=-/etc/sysconfig/wpa_supplicant
ExecStart=/usr/sbin/wpa_supplicant -u -f /var/log/wpa_supplicant.log -c /etc/wpa_supplicant/wpa_supplicant.conf $INTERFACES $DRIVERS $OTHER_ARGS

[Install]
WantedBy=multi-user.target