qa/src/multithread2.c: don't use PM_CONTEXT_LOCAL

This test application only needs a context to initialize some mutexes.

PM_CONTEXT_LOCAL seemed like a good light-weight choice, until
the Linux proc PMDA was added to PM_CONTEXT_LOCAL at which point
pmNewContext() ends up initializing the hotproc metrics which calls
__pmAFregister() before any thread creation in multithread2.c ... and
this totally screws the cleverly orchestrated dance between the two
threads in this app.

Changing to PM_CONTEXT_HOST for the "local:" host restored the qa
tests 449 and 1074 to passing.

qa/src/multithread2.c

@@ -197,7 +197,7 @@ main()
     }
 
     /* only need this to initialize library mutexes */
-    if ((sts = pmNewContext(PM_CONTEXT_LOCAL, NULL)) < 0) {
+    if ((sts = pmNewContext(PM_CONTEXT_HOST, "local:")) < 0) {
 	printf("pmNewContext: %s\n", pmErrStr(sts));
 	exit(1);
     }