fixfiles: use grep -F when search in mounts

systemd escapes luks uid so that mount points contain '\' and grep
should not consider this as regexp
Fixes:
    $ cat /proc/self/mounts | sort | uniq | awk '{print $2}'
    /run/credentials/systemd-cryptsetup@luks\134x2d6d1f41e6\134x2d5538\134x2d41a0\134x2db383\134x2cd41c2ddcacaa.service

    $ sudo fixfiles -B onboot
    grep: Invalid back reference
    grep: Invalid back reference
    System will relabel on next boot

Suggested-by: Christopher Tubbs <ctubbsii@fedoraproject.org>
Signed-off-by: Petr Lautrbach <lautrbach@redhat.com>
Acked-by: James Carter <jwcart2@gmail.com>

policycoreutils/scripts/fixfiles

@@ -45,24 +45,24 @@ FS="`cat /proc/self/mounts | sort | uniq | awk '{print $2}'`"
 for i in $FS; do
 	if [ `useseclabel` -ge 0 ]
 	then
-		grep " $i " /proc/self/mounts | awk '{print $4}' | grep -E --silent '(^|,)seclabel(,|$)' && echo $i
+		grep -F " $i " /proc/self/mounts | awk '{print $4}' | grep -E --silent '(^|,)seclabel(,|$)' && echo $i
 	else
-		grep " $i " /proc/self/mounts | grep -v "context=" | grep -E --silent '(ext[234]| ext4dev | gfs2 | xfs | jfs | btrfs )' && echo $i
+		grep -F " $i " /proc/self/mounts | grep -v "context=" | grep -E --silent '(ext[234]| ext4dev | gfs2 | xfs | jfs | btrfs )' && echo $i
 	fi
 done
 }
 
 get_rw_labeled_mounts() {
 FS=`get_all_labeled_mounts | sort | uniq`
 for i in $FS; do
-	grep " $i " /proc/self/mounts | awk '{print $4}' | grep -E --silent '(^|,)rw(,|$)' && echo $i
+	grep -F " $i " /proc/self/mounts | awk '{print $4}' | grep -E --silent '(^|,)rw(,|$)' && echo $i
 done
 }
 
 get_ro_labeled_mounts() {
 FS=`get_all_labeled_mounts | sort | uniq`
 for i in $FS; do
-	grep " $i " /proc/self/mounts | awk '{print $4}' | grep -E --silent '(^|,)ro(,|$)' && echo $i
+	grep -F " $i " /proc/self/mounts | awk '{print $4}' | grep -E --silent '(^|,)ro(,|$)' && echo $i
 done
 }