process-util: move fork_agent() to process-util.[ch]

It's a relatively small wrapper around safe_fork() now, hence let's move
it over, and make its signature even more alike. Also, set a different
process name for the polkit and askpw agents.

src/shared/spawn-ask-password-agent.c

@@ -40,8 +40,9 @@ int ask_password_agent_open(void) {
         if (!isatty(STDIN_FILENO))
                 return 0;
 
-        r = fork_agent(&agent_pid,
+        r = fork_agent("(sd-askpwagent)",
                        NULL, 0,
+                       &agent_pid,
                        SYSTEMD_TTY_ASK_PASSWORD_AGENT_BINARY_PATH,
                        SYSTEMD_TTY_ASK_PASSWORD_AGENT_BINARY_PATH, "--watch", NULL);
         if (r < 0)

src/shared/spawn-polkit-agent.c

@@ -38,9 +38,8 @@
 static pid_t agent_pid = 0;
 
 int polkit_agent_open(void) {
-        int r;
-        int pipe_fd[2];
         char notify_fd[DECIMAL_STR_MAX(int) + 1];
+        int pipe_fd[2], r;
 
         if (agent_pid > 0)
                 return 0;
@@ -49,8 +48,7 @@ int polkit_agent_open(void) {
         if (geteuid() == 0)
                 return 0;
 
-        /* We check STDIN here, not STDOUT, since this is about input,
-         * not output */
+        /* We check STDIN here, not STDOUT, since this is about input, not output */
         if (!isatty(STDIN_FILENO))
                 return 0;
 
@@ -59,8 +57,9 @@ int polkit_agent_open(void) {
 
         xsprintf(notify_fd, "%i", pipe_fd[1]);
 
-        r = fork_agent(&agent_pid,
+        r = fork_agent("(polkit-agent)",
                        &pipe_fd[1], 1,
+                       &agent_pid,
                        POLKIT_AGENT_BINARY_PATH,
                        POLKIT_AGENT_BINARY_PATH, "--notify-fd", notify_fd, "--fallback", NULL);