FLAG-81: fixed the exception in evaluate all flags

[ManojLL]

Description of what I changed

I updated the flagService.evaluateAllFlags method to invoke the patient flag task thread when evaluating all flags, which then call PatientFlagTask.evaluateAllFlags(). Previously, the flagService.evaluateAllFlags() method directly called the PatientFlagTask.evaluateAllFlags() method, that causing to invoke two PatinetFlagTask threads.

This change also fixed the duplicate patient flag issue.

Issue I worked on

see https://openmrs.atlassian.net/browse/FLAG-81

Checklist: I completed these to help reviewers :)

• My IDE is configured to follow the code style of this project.

  No? Unsure? -> configure your IDE, format the code and add the changes with git add . && git commit --amend

• I have added tests to cover my changes. (If you refactored
  existing code that was well tested you do not have to add tests)

  No? -> write tests and add them to this commit git add . && git commit --amend

• I ran mvn clean package right before creating this pull request and
  added all formatting changes to my commit.

  No? -> execute above command

• All new and existing tests passed.

  No? -> figure out why and add the fix to your commit. It is your responsibility to make sure your code works.

• My pull request is based on the latest changes of the master branch.

  No? Unsure? -> execute command git pull --rebase upstream master

[wikumChamith]

why do these methods get merged?

[ManojLL]

I created generatePatientFalgsForFalgAndPatient(..) method in this PR and this used to generate patient flags without deleting the existing patient flag. With the new changes we can use generatePatientFlags(Flag flag) method.