Make testcase 2372 work on SunOS

Since SunOS needs a litt bit more workspace_thread, this test case
needs to be updated.

The default buffer size for vtc (configurable with -b) had to be
increased.

bin/varnishtest/tests/r02372.vtc

 varnishtest "Count purges when there are many variants"
 
-server s1 -repeat 40 {
+server s1 -repeat 72 {
 	rxreq
 	txresp -hdr "Vary: foo"
 } -start
 
-varnish v1 -arg "-p workspace_thread=256" -vcl+backend {
+varnish v1 -arg "-p workspace_thread=512" -vcl+backend {
 	import std;
 
 	sub vcl_recv {
@@ -16,7 +16,7 @@ varnish v1 -arg "-p workspace_thread=256" -vcl+backend {
 	}
 } -start
 
-client c1 -repeat 40 {
+client c1 -repeat 72 {
 	txreq
 	rxresp
 } -run
@@ -29,4 +29,4 @@ client c2 {
 varnish v1 -expect n_lru_nuked == 0
 varnish v1 -expect cache_hit == 0
 varnish v1 -expect n_purges == 1
-varnish v1 -expect n_obj_purged == 40
+varnish v1 -expect n_obj_purged == 72

bin/varnishtest/vtc_main.c

@@ -79,7 +79,7 @@ struct vtc_job {
 
 int iflg = 0;
 unsigned vtc_maxdur = 60;
-static unsigned vtc_bufsiz = 512 * 1024;
+static unsigned vtc_bufsiz = 1024 * 1024;
 
 static VTAILQ_HEAD(, vtc_tst) tst_head = VTAILQ_HEAD_INITIALIZER(tst_head);
 static struct vev_base *vb;