[GOBBLIN-461] disabling PasswordManagerTests as they fail often on travis

[arjun4084346]

Dear Gobblin maintainers,

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

JIRA

• My PR addresses the following
  • https://issues.apache.org/jira/browse/GOBBLIN-461

Description

• Here are some details about my PR, including screenshots (if applicable):
  These tests were disabled before; but recently enabled again

57a6566#diff-ef5fa9697f5bdd44cfa577f2ed2b869aL36

and since then they fail often.

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason: not needed as this is adding no new source code

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"