selinux: Chain up tool resolving errors in install_policy.sh

Subshell evaluations are not exempt from errexit, so if a command is
not available, `which` will fail and exit the script as a whole.
This causes the helpful error messages to not be printed if they are
tacked on using a `$?` comparison.

Resolve the issue by using chains of logical operators, which are not
subject to the effects of errexit.

Fixes: e37c187 ("scripts/selinux: modernize mdp")
Signed-off-by: Tim Schumacher <tim.schumacher1@huawei.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

Author: schmchrt

scripts/selinux/install_policy.sh

@@ -6,27 +6,24 @@ if [ `id -u` -ne 0 ]; then
 	exit 1
 fi
 
-SF=`which setfiles`
-if [ $? -eq 1 ]; then
+SF=`which setfiles` || {
 	echo "Could not find setfiles"
 	echo "Do you have policycoreutils installed?"
 	exit 1
-fi
+}
 
-CP=`which checkpolicy`
-if [ $? -eq 1 ]; then
+CP=`which checkpolicy` || {
 	echo "Could not find checkpolicy"
 	echo "Do you have checkpolicy installed?"
 	exit 1
-fi
+}
 VERS=`$CP -V | awk '{print $1}'`
 
-ENABLED=`which selinuxenabled`
-if [ $? -eq 1 ]; then
+ENABLED=`which selinuxenabled` || {
 	echo "Could not find selinuxenabled"
 	echo "Do you have libselinux-utils installed?"
 	exit 1
-fi
+}
 
 if selinuxenabled; then
     echo "SELinux is already enabled"