detect meru as a BMC-lite platform

Summary: We should automate this with platforms.json somehow but no time right now.

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/bletchley      (cached)
?       github.com/facebook/openbmc/tools/flashy/flash_procedure        [no test files]
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/lib/logger     [no test files]
?       github.com/facebook/openbmc/tools/flashy/utilities      [no test files]
?       github.com/facebook/openbmc/tools/flashy/tests  [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)
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)
```

Reviewed By: cjcon90

Differential Revision: D51814249

fbshipit-source-id: 45a3f7735178dd8aa5e44f3c5715e317b646d0a7

tools/flashy/lib/utils/system.go

@@ -368,14 +368,19 @@ var IsLFOpenBMC = func() (bool) {
 // IsBMCLite check whether the system is running BMC-lite
 // For S368275.   Make this beautiful later.
 var IsBMCLite = func() (bool) {
-	const magic = "fbdarwin"
+	magics := []string{"fbdarwin", "meru"}
 
 	issueBuf, err := fileutils.ReadFile(etcIssueFilePath)
 	if err != nil {
 		return false
 	}
 
-	return strings.Contains(string(issueBuf), magic)
+	for _, magic := range magics {
+		if strings.Contains(string(issueBuf), magic) {
+			return true;
+		}
+	}
+	return false
 }
 
 // CheckOtherFlasherRunning return an error if any other flashers are running.