Stringify query params which are objects as JSON [2.x]

[horiaradu]

This is a backport of this PR: #325. I've cherrypicked the commit and so I've added the refactorings which were made in the test file as well.

@gunjpan - check it out :)

[slnode]

Can one of the admins verify this patch? To accept patch and trigger a build add comment ".ok\W+to\W+test."

[slnode]

Can one of the admins verify this patch?

[slnode]

Can one of the admins verify this patch?

[slnode]

Can one of the admins verify this patch?

[gunjpan]

@slnode ok to test

[gunjpan]

@horiaradu : Change LGTM. Could you please update commit message to say: backport of PR#325
For example, PTAL at this: https://github.com/strongloop/loopback/pull/2782/commits

[gunjpan]

@horiaradu : Thank you for updating the commit message, but now it breaks the CI with:

Linting commit logs
**
**  1 problems found:
**    2323ddc - Stringify query params which are objects as JSON [2: First line should be 50 characters or less (saw 54)

Also, backport of #<PR number> should be a PR #325, instead of the issue where it was reported as bug.
Could you please fix it. Thank you.

[gunjpan]

@horiaradu: Landed. Thank you for the PR and keeping up with change requests.