qemu-ga: Handle errors uniformely in ga_channel_open()

We detect errors in several places.  One reports with g_error(), which
calls abort(), the others report with g_critical().  Three of them
exit(), three return false.

Always report with g_critical(), and return false.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMichael Roth <mdroth@linux.vnet.ibm.com>
Reviewed-by: NLuiz Capitulino <lcapitulino@redhat.com>

*minor fix-up of commit msg
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

qga/channel-posix.c

@@ -141,14 +141,15 @@ static gboolean ga_channel_open(GAChannel *c, const gchar *path, GAChannelMethod
                            );
         if (fd == -1) {
             g_critical("error opening channel: %s", strerror(errno));
-            exit(EXIT_FAILURE);
+            return false;
         }
 #ifdef CONFIG_SOLARIS
         ret = ioctl(fd, I_SETSIG, S_OUTPUT | S_INPUT | S_HIPRI);
         if (ret == -1) {
             g_critical("error setting event mask for channel: %s",
                        strerror(errno));
-            exit(EXIT_FAILURE);
+            close(fd);
+            return false;
         }
 #endif
         ret = ga_channel_client_add(c, fd);
@@ -164,7 +165,7 @@ static gboolean ga_channel_open(GAChannel *c, const gchar *path, GAChannelMethod
         int fd = qemu_open(path, O_RDWR | O_NOCTTY | O_NONBLOCK);
         if (fd == -1) {
             g_critical("error opening channel: %s", strerror(errno));
-            exit(EXIT_FAILURE);
+            return false;
         }
         tcgetattr(fd, &tio);
         /* set up serial port for non-canonical, dumb byte streaming */
@@ -184,7 +185,9 @@ static gboolean ga_channel_open(GAChannel *c, const gchar *path, GAChannelMethod
         tcsetattr(fd, TCSANOW, &tio);
         ret = ga_channel_client_add(c, fd);
         if (ret) {
-            g_error("error adding channel to main loop");
+            g_critical("error adding channel to main loop");
+            close(fd);
+            return false;
         }
         break;
     }