tests: Use "command -v" instead of which(1) in shell scripts

When which(1) is not installed, we would complain "perl not found"
because it's the first set_prog_path check. The error message is
wrong.

Fix it by using "command -v", a native way to query the existence of a
command.
Suggested-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NFam Zheng <famz@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Message-id: 1416380832-9697-1-git-send-email-famz@redhat.com
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/common

@@ -289,10 +289,10 @@ testlist options
 
             if [ ! -z "$DISPLAY" ]
             then
-                which xdiff >/dev/null 2>&1 && diff=xdiff
-                which gdiff >/dev/null 2>&1 && diff=gdiff
-                which tkdiff >/dev/null 2>&1 && diff=tkdiff
-                which xxdiff >/dev/null 2>&1 && diff=xxdiff
+                command -v xdiff >/dev/null 2>&1 && diff=xdiff
+                command -v gdiff >/dev/null 2>&1 && diff=gdiff
+                command -v tkdiff >/dev/null 2>&1 && diff=tkdiff
+                command -v xxdiff >/dev/null 2>&1 && diff=xxdiff
             fi
             ;;
 

tests/qemu-iotests/common.config

@@ -47,7 +47,7 @@ export PWD=`pwd`
 # $1 = prog to look for, $2* = default pathnames if not found in $PATH
 set_prog_path()
 {
-    p=`which $1 2> /dev/null`
+    p=`command -v $1 2> /dev/null`
     if [ -n "$p" -a -x "$p" ]; then
         echo $p
         return 0