Makefile is not properly handling shellscript description

[ymotongpoo]

Makefile in the project root is not handling shellscript and is causing unexpected behaviour, such as:

• the check of existing cluster always fails because the value of EXISTING_CLUSTER is not passed to the if validation
• RATING_SERVICE_ADDR is not passed to the following line because of the lack of continuation

The error message around RATING_SERVICE_ADDR:

...
- deployment/frontend: container server terminated with exit code 2
    - pod/frontend-6595944855-rsw4m: container server terminated with exit code 2
      > [frontend-6595944855-rsw4m server] {"time":"2021-06-03T23:51:53.773692059Z","updates":null}
      > [frontend-6595944855-rsw4m server] panic: environment variable "RATING_SERVICE_ADDR" not set
      > [frontend-6595944855-rsw4m server] goroutine 1 [running]:
      > [frontend-6595944855-rsw4m server] main.mustMapEnv(0xc0003820a8, 0xb065ef, 0x13)
      > [frontend-6595944855-rsw4m server]      /go/src/github.com/GoogleCloudPlatform/microservices-demo/src/frontend/main.go:297 +0x10b
      > [frontend-6595944855-rsw4m server] main.main()
      > [frontend-6595944855-rsw4m server]      /go/src/github.com/GoogleCloudPlatform/microservices-demo/src/frontend/main.go:149 +0xae9
 - deployment/frontend failed. Error: container server terminated with exit code 2.
9/11 deployment(s) failed
make: *** [Makefile:26: cluster] Error 1