kdump-lib: make is_zstd_command_available more generic

There is value to use the function in other places as well. For example
it can be used to check whether optional dependencies, like grubby, are
installed. Thus make it more generic so it can be reused in later
commits.

Signed-off-by: Philipp Rudo <prudo@redhat.com>
Reviewed-by: Pingfan Liu <piliu@redhat.com>

kdump-lib.sh

@@ -48,9 +48,9 @@ is_squash_available()
 	done
 }
 
-is_zstd_command_available()
+has_command()
 {
-	[[ -x "$(command -v zstd)" ]]
+	[[ -x $(command -v "$1") ]]
 }
 
 dracut_have_option()

mkdumprd

@@ -443,7 +443,7 @@ handle_default_dump_target
 if ! have_compression_in_dracut_args; then
 	if is_squash_available && dracut_have_option "--squash-compressor"; then
 		add_dracut_arg "--squash-compressor" "zstd"
-	elif is_zstd_command_available; then
+	elif has_command zstd; then
 		add_dracut_arg "--compress" "zstd"
 	fi
 fi

mkfadumprd

@@ -64,7 +64,7 @@ _dracut_isolate_args=(
 
 # Use zstd compression method, if available
 if ! have_compression_in_dracut_args; then
-	if is_zstd_command_available; then
+	if has_command zstd; then
 		_dracut_isolate_args+=(--compress zstd)
 	fi
 fi