Fix resource leaks identified by cppcheck

* Where possible rearrange error checks to avoid branching
* Otherwise add missing `fclose`, `close`, `px4_close` calls before return

src/systemcmds/tests/test_file2.c

@@ -133,12 +133,14 @@ static void test_corruption(const char *filename, uint32_t write_chunk, uint32_t
 
 		if (read(fd, buffer, sizeof(buffer)) != (int)sizeof(buffer)) {
 			printf("read failed at offset %u\n", ofs);
+			close(fd);
 			return;
 		}
 
 		for (uint16_t j = 0; j < write_chunk; j++) {
 			if (buffer[j] != get_value(ofs)) {
 				printf("corruption at ofs=%u got %u\n", ofs, buffer[j]);
+				close(fd);
 				return;
 			}
 

src/systemcmds/tests/test_mount.c

@@ -158,6 +158,7 @@ test_mount(int argc, char *argv[])
 		}
 
 		if (it_left_abort == 0) {
+			px4_close(cmd_fd);
 			(void)unlink(cmd_filename);
 			return 0;
 		}

src/systemcmds/tests/test_ppm_loopback.c

@@ -79,6 +79,8 @@ int test_ppm_loopback(int argc, char *argv[])
 
 	if (result != OK) {
 		warnx("PWM_SERVO_GET_COUNT");
+
+		(void)close(servo_fd);
 		return ERROR;
 	}
 

src/systemcmds/tests/test_uart_loopback.c

@@ -68,13 +68,14 @@ int test_uart_loopback(int argc, char *argv[])
 	int stdout_fd = 1;
 
 	int uart2 = open("/dev/ttyS1", O_RDWR | O_NONBLOCK | O_NOCTTY);
-	int uart5 = open("/dev/ttyS2", O_RDWR | O_NONBLOCK | O_NOCTTY);
 
 	if (uart2 < 0) {
 		printf("ERROR opening UART2, aborting..\n");
 		return uart2;
 	}
 
+	int uart5 = open("/dev/ttyS2", O_RDWR | O_NONBLOCK | O_NOCTTY);
+
 	if (uart5 < 0) {
 		if (uart2 >= 0) {
 			close(uart2);