Fix missing quotes for possibly unresolved variables in shell test-statements

Related: OS#5736

Change-Id: I7e7f4f95d1a7cc886360c733908c63a2843b0906

ttcn3-dumpcap-start.sh

@@ -30,7 +30,7 @@ fi
 kill_rm_pidfile $PIDFILE_NETCAT
 kill_rm_pidfile $PIDFILE_PCAP
 
-if [ ! -x $DUMPCAP ]; then
+if [ ! -x "$DUMPCAP" ]; then
 	echo "Missing required dumpcap binary at ${DUMPCAP}"
 	exit 31
 fi

ttcn3-tcpdump-start.sh

@@ -35,7 +35,7 @@ else
 	CMD="sudo $TCPDUMP -U"
 fi
 
-if [ -x $DUMPCAP ]; then
+if [ -x "$DUMPCAP" ]; then
     CAP_ERR="1"
     if [ -x /sbin/setcap ]; then
 	# N. B: this check requires libcap2-bin package