Merge release332 branch to release branch for SonarQube cache

[abitmore]

See #2096.

The Travis build status and link for continuous-integration/travis-ci/pr showing in the PR is sometimes incorrect. The correct link for this PR is https://travis-ci.org/bitshares/bitshares-core/builds/647351439. It didn't pass. Retry after merged #2097.

[abitmore]

The cache in master branch didn't help. Investigating.

[abitmore]

There might be some issues or limitations with SonarQube CFamily cache, but the documentation is a bit poor. The feature is relatively new though. Only found a question here: https://community.sonarsource.com/t/cfamily-cache-limitations/19870, but no answer.

Steps I've tried:

• built master branch and populated a cache;
• created a new branch abitmore-travis-cache-test-master from master, the scanner reported 100% cache hit;
• created a new branch abitmore-travis-cache-test from testnet, although lots of files are identical to master, the scanner reported no cache hit before being terminated in the middle.

Here are logs in Travis:

• https://travis-ci.org/bitshares/bitshares-core/jobs/647722953
  INFO: Cache hit for: /home/travis/build/bitshares/bitshares-core/libraries/utilities/key_conversion.cpp
• https://travis-ci.org/bitshares/bitshares-core/jobs/647689690
  INFO: [pool-3-thread-1] /home/travis/build/bitshares/bitshares-core/libraries/utilities/key_conversion.cpp

Still investigating.

[abitmore]

No progress about the cache.

To get Travis work in release, testnet and master, I will port #2039 to release branch for next release.

[abitmore]

All tests passed but SonarQube scanner didn't finish. Merging to benefit future pull requests.