backpatch "Set application_name per-test in isolation and ecpg tests."

We started to backpatch test infrastructure improvements more aggressively to
make it easier to backpatch test. A proposed isolationtester improvement has a
dependency on b1907d688, backpatch b1907d688 to make it easier to subsequently
backpatch the new proposed isolationtester change.

Discussion: https://postgr.es/m/861977.1639421872@sss.pgh.pa.us
Backpatch: 10-12, the commit already is in 13-HEAD

src/interfaces/ecpg/test/pg_regress_ecpg.c

@@ -95,6 +95,7 @@ ecpg_start_test(const char *testname,
 				expectfile_source[MAXPGPATH];
 	char		cmd[MAXPGPATH * 3];
 	char	   *testname_dash;
+	char	   *appnameenv;
 
 	snprintf(inprg, sizeof(inprg), "%s/%s", inputdir, testname);
 
@@ -144,6 +145,9 @@ ecpg_start_test(const char *testname,
 			 outfile_stdout,
 			 outfile_stderr);
 
+	appnameenv = psprintf("PGAPPNAME=ecpg/%s", testname_dash);
+	putenv(appnameenv);
+
 	pid = spawn_process(cmd);
 
 	if (pid == INVALID_PID)
@@ -153,6 +157,10 @@ ecpg_start_test(const char *testname,
 		exit(2);
 	}
 
+	unsetenv("PGAPPNAME");
+	free(appnameenv);
+
+	free(testname_dash);
 	free(outfile_stdout);
 	free(outfile_stderr);
 	free(outfile_source);

src/test/isolation/isolation_main.c

@@ -36,6 +36,7 @@ isolation_start_test(const char *testname,
 	char		expectfile[MAXPGPATH];
 	char		psql_cmd[MAXPGPATH * 3];
 	size_t		offset = 0;
+	char	   *appnameenv;
 
 	/* need to do the path lookup here, check isolation_init() for details */
 	if (!looked_up_isolation_exec)
@@ -97,6 +98,9 @@ isolation_start_test(const char *testname,
 		exit(2);
 	}
 
+	appnameenv = psprintf("PGAPPNAME=isolation/%s", testname);
+	putenv(appnameenv);
+
 	pid = spawn_process(psql_cmd);
 
 	if (pid == INVALID_PID)
@@ -106,6 +110,9 @@ isolation_start_test(const char *testname,
 		exit(2);
 	}
 
+	unsetenv("PGAPPNAME");
+	free(appnameenv);
+
 	return pid;
 }
 

src/test/regress/pg_regress.c

@@ -726,6 +726,10 @@ doputenv(const char *var, const char *val)
 static void
 initialize_environment(void)
 {
+	/*
+	 * Set default application_name.  (The test_function may choose to
+	 * override this, but if it doesn't, we have something useful in place.)
+	 */
 	putenv("PGAPPNAME=pg_regress");
 
 	if (nolocale)