Update the manual with new default

My previous patch did not update the manual and the usage message for
varnishtest concerning the default internal buffer size.

bin/varnishtest/vtc_main.c

@@ -128,7 +128,7 @@ usage(void)
 	fprintf(stderr, "usage: varnishtest [options] file ...\n");
 #define FMT "    %-28s # %s\n"
 	fprintf(stderr, FMT, "-b size",
-	    "Set internal buffer size (default: 512K)");
+	    "Set internal buffer size (default: 1M)");
 	fprintf(stderr, FMT, "-D name=val", "Define macro");
 	fprintf(stderr, FMT, "-i", "Find varnish binaries in build tree");
 	fprintf(stderr, FMT, "-j jobs", "Run this many tests in parallel");

doc/sphinx/reference/varnishtest.rst

@@ -30,7 +30,7 @@ simulate a transaction to provoke a specific behavior.
 
 The following options are available:
 
--b size          Set internal buffer size (default: 512K)
+-b size          Set internal buffer size (default: 1M)
 
 -D name=val      Define macro for use in scripts