Statuses.valueOf instead of checking against all the enum values

[fractalliter]

https://github.com/benwilcock/spring-cloud-stream-demo/blob/fbdadd1b8d30c5f3d42c18e03835474aaa052f29/loancheck/src/main/java/io/pivotal/loancheck/Loan.java#L34-L38

https://github.com/benwilcock/spring-cloud-stream-demo/blob/fbdadd1b8d30c5f3d42c18e03835474aaa052f29/loansource/src/main/java/io/pivotal/loansource/Loan.java#L37-L46

Instead of all checking against all of the Statuses enum values, we can easily check the existence of the status with the help of Statuses.valueOf which throws IllegalArgumentException as well.

try {
      this.status = Statuses.valueOf(status).name();
} catch (IllegalArgumentException ex){
      throw new IllegalArgumentException("Cannot set the LoanApplication's status to " + status);
}