s390-tools: Replace 'which' with built-in 'command -v'

There are still a few scripts using the 'which' command to determine
either the full path or the mere existence of an executable.
Some of these scripts might run in minimal environments where 'which' is
not available due to dependency restriction. 'which' is also considered
unreliable for historical implementation details.

Use the POSIX defined [1] built-in 'command -v' instead to reduce
package dependencies and improve reliability.

[1] https://pubs.opengroup.org/onlinepubs/9699919799/
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>

iucvterm/doc/ts-shell/iucvconn_on_login

@@ -15,7 +15,7 @@
 prog_name=`basename $0`
 guest_name=${USER:-`whoami 2>/dev/null`}
 terminal=lnxhvc0
-iucvconn=`which iucvconn 2>/dev/null`
+iucvconn=`command -v iucvconn 2>/dev/null`
 
 __error() {
 	printf "$prog_name: $@\n" >&2

netboot/mk-pxelinux-ramfs

@@ -127,7 +127,7 @@ echo "$cmd: Copying kexec"
 # Install both binary and required shared libraries
 OLDPATH=$PATH
 PATH=$OLDPATH:/sbin:/usr/sbin
-kexec_bin=$(which kexec)
+kexec_bin=$(command -v kexec)
 kexec_sos=$(sharedobjs $kexec_bin)
 PATH=$OLDPATH
 

ziomon/ziomon

@@ -667,8 +667,7 @@ function check_free_space_mileage() {
 
 
 function check_blktrace() {
-   which blktrace >/dev/null 2>&1;
-   if [ $? -ne 0 ]; then
+   if ! command -v blktrace >/dev/null 2>&1; then
       echo "$WRP_TOOLNAME: Could not find blktrace. Please make sure that the blktrace package is installed and matches the level in the documentation.";
       exit 1;
    fi