RFR: 7820: Add validations for master password [v4]

[Suchita Chaturvedi]

> This PR adds password validations for master password field.

Suchita Chaturvedi has updated the pull request incrementally with one additional commit since the last revision:

  Minor modifications as per review

-------------

Changes:
  - all: https://git.openjdk.org/jmc/pull/406/files
  - new: https://git.openjdk.org/jmc/pull/406/files/ba4bbfa3..0bce856a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jmc&pr=406&range=03
 - incr: https://webrevs.openjdk.org/?repo=jmc&pr=406&range=02-03

  Stats: 4 lines in 2 files changed: 0 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jmc/pull/406.diff
  Fetch: git fetch https://git.openjdk.org/jmc pull/406/head:pull/406

PR: https://git.openjdk.org/jmc/pull/406