GOBBLIN-670: Ensure MultiHopFlowCompiler is initialized when job template catalog location is not provided.

[sv2000]

Dear Gobblin maintainers,

Please accept this PR. I understand that it will not be reviewed until I have checked off all the steps below!

JIRA

• My PR addresses the following Gobblin JIRA issues and references them in the PR title. For example, "[GOBBLIN-XXX] My Gobblin PR"
  • https://issues.apache.org/jira/browse/GOBBLIN-670

Description

• Here are some details about my PR, including screenshots (if applicable):
  Initialization of Gobblin service with MultiHopFlowCompiler should succeed even when job templates location is not provided or is empty. Currently, the initialization fails due to exception encountered when initializing the JobCatalog.

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:
  Tested in local environment.

Commits

• My commits all reference JIRA issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

[htran1]

+1