detect missing/broken flash chips on non-vboot

Summary:
If the U-Boot environment (env MTD partition) is inaccessible and flash0 is
missing too, it's a good indication that something serious is amiss with the
SPI chips.  Return a  broken flash chip error code in this case, instead of
an unsafe to reboot error.

(For example an A-SPEED/Linux driver bug may hide the env partition on the
primary chip invisible if the secondary chip is inaccessible.)

Test Plan:
Build & unit test:

```
0 ~/local/openbmc/tools/flashy $ ./build.sh && ./build_dev.sh && go test ./...
ok      github.com/facebook/openbmc/tools/flashy        (cached)
ok      github.com/facebook/openbmc/tools/flashy/checks_and_remediations/common (cached)
ok      github.com/facebook/openbmc/tools/flashy/checks_and_remediations/galaxy100      (cached)
ok      github.com/facebook/openbmc/tools/flashy/checks_and_remediations/wedge100       (cached)
ok      github.com/facebook/openbmc/tools/flashy/checks_and_remediations/yamp   (cached)
?       github.com/facebook/openbmc/tools/flashy/flash_procedure        [no test files]
ok      github.com/facebook/openbmc/tools/flashy/install        (cached)
ok      github.com/facebook/openbmc/tools/flashy/lib/fileutils  (cached)
ok      github.com/facebook/openbmc/tools/flashy/lib/flash      (cached)
ok      github.com/facebook/openbmc/tools/flashy/lib/flash/flashcp      (cached)
ok      github.com/facebook/openbmc/tools/flashy/lib/flash/flashutils   (cached)
ok      github.com/facebook/openbmc/tools/flashy/lib/flash/flashutils/devices   (cached)
?       github.com/facebook/openbmc/tools/flashy/lib/logger     [no test files]
ok      github.com/facebook/openbmc/tools/flashy/lib/step       (cached)
ok      github.com/facebook/openbmc/tools/flashy/lib/utils      (cached)
ok      github.com/facebook/openbmc/tools/flashy/lib/validate   (cached)
ok      github.com/facebook/openbmc/tools/flashy/lib/validate/image     (cached)
ok      github.com/facebook/openbmc/tools/flashy/lib/validate/partition (cached)
?       github.com/facebook/openbmc/tools/flashy/tests  [no test files]
?       github.com/facebook/openbmc/tools/flashy/utilities      [no test files]
0 ~/local/openbmc/tools/flashy $ echo $?
0
```

Reviewed By: kawmarco

fbshipit-source-id: 355a7d01ce55f4994ca76693b360592206651b6a

tools/flashy/checks_and_remediations/common/04_ensure_flash_available.go

@@ -72,6 +72,12 @@ func ensureFlashAvailable(stepParams step.StepParams) step.StepExitError {
 	cmd = []string{"fw_printenv", "bootargs"}
 	_, err, stdout, stderr = utils.RunCommand(cmd, 30*time.Second)
 	if err != nil {
+		if strings.Contains(stderr, "Cannot access MTD device") {
+			errMsg := errors.Errorf(
+				"U-Boot environment is inaccessible: broken flash chip?" +
+				" Error code: %v, stderr: %v", err, stderr)
+			return step.ExitBadFlashChip{Err: errMsg}
+		}
 		log.Printf("fw_printenv doesn't work: %v, stderr: %v", err, stderr)
 		return nil
 	}

tools/flashy/checks_and_remediations/common/04_ensure_flash_available_test.go

@@ -86,15 +86,25 @@ func TestEnsureFlashAvailable(t *testing.T) {
 			want:              step.ExitMustReboot{Err: errors.Errorf("Forcing reboot for new bootargs to take effect")},
 		},
 		{
-			name:              "fw_printenv broken",
+			name:              "fw_printenv broken because reasons",
 			vbootUtilExists:   false,
 			failGrep:          false,
 			failPrint:         true,
 			failSet:           false,
-			printOutput:       "lol",
-			grepOutput:        "mtd4: 02000000 00010000 \"flash0\"",
+			printOutput:       "",
+			grepOutput:        "",
 			want:              nil,
 		},
+		{
+			name:              "fw_printenv broken because missing flash",
+			vbootUtilExists:   false,
+			failGrep:          false,
+			failPrint:         true,
+			failSet:           false,
+			printOutput:       "Cannot access MTD device /dev/mtd1: No such file or directory",
+			grepOutput:        "",
+			want:              step.ExitBadFlashChip{Err: errors.Errorf("U-Boot environment is inaccessible: broken flash chip? Error code: err1, stderr: Cannot access MTD device /dev/mtd1: No such file or directory")},
+		},
 		{
 			name:              "fw_setenv broken",
 			vbootUtilExists:   false,
@@ -121,9 +131,9 @@ func TestEnsureFlashAvailable(t *testing.T) {
 					}
 				} else if (cmdArr[0] == "fw_printenv") {
 					if (tc.failPrint) {
-						return 0, errors.Errorf("err1"), "", "err1"
+						return 1, errors.Errorf("err1"), "", tc.printOutput
 					} else {
-						return 0, nil, tc.printOutput, ""
+						return 0, nil, "", tc.printOutput
 					}
 				} else if (cmdArr[0] == "fw_setenv") {
 					if (tc.failSet) {