test: add check for wrk to test-keep-alive

test/pummel/test-keep-alive.js requires `wrk` to be installed. Check if
it is, and skip the test if it isn't.
This is yet another step in preparation for running pummel tests in CI
daily.
PR-URL: #25516
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: Trott

test/pummel/test-keep-alive.js

@@ -23,11 +23,13 @@
 
 // This test requires the program 'wrk'.
 constcommon=require('../common');
-if(common.isWindows)
-common.skip('no `wrk` on windows');
+
+constchild_process=require('child_process');
+constresult=child_process.spawnSync('wrk',['-h']);
+if(result.error&&result.error.code==='ENOENT')
+common.skip('test requires `wrk` to be installed first');
 
 constassert=require('assert');
-constspawn=require('child_process').spawn;
 consthttp=require('http');
 consturl=require('url');
 
@@ -60,7 +62,7 @@ const runAb = (opts, callback) => {
 args.push(url.format({hostname: '127.0.0.1',
 port: opts.port,protocol: 'http'}));
 
-constchild=spawn('wrk',args);
+constchild=child_process.spawn('wrk',args);
 child.stderr.pipe(process.stderr);
 child.stdout.setEncoding('utf8');