Fix WebAPI issues

[wblachowski]

I fixed some inconsistencies in WebAPI responses and provided more meaningful 404 messages.

Closes #425

Description

Issues addressed:

1. Get artifact by artifactId for wrong artifactId:
   http://aet-vagrant:8181/api/artifact?company=company&project=project&id=99999999

• Old response:
  500
• New response:
  404

  {
  "message": "Unable to get artifact with id: 99999999 for {company='company', project='project'}"
  }

2. Get metadata for wrong correlationId
   http://aet-vagrant:8181/api/artifact?company=company&project=project&id=99999999

• Old response:
  400

  {
  "message": "Unable to get Suite Metadata for {company='company', project='project'}"
  {

• New response:
  404

  {
  "message": "Unable to get Suite Metadata with correlationId: 99999999 for {company='company', project='project'}"
  }

3. Get metadata for wrong suite name
   http://aet-vagrant:8181/api/metadata?company=company&project=project&suite=no_existing_suite

• Old response:
  400

  {
  "message": "Unable to get Suite Metadata for {company='company', project='project'}"
  }

• New response:
  404

  {
  "message": "Unable to get Suite Metadata with suite name: no_existing_suite for {company='company', project='project'}"
  }

4. Get metadata by suite name and wrong version
   http://aet-vagrant:8181/api/metadata?company=company&project=project&suite=test-suite&version=999

• Old response:
  400

  {
  "message": "Unable to get Suite Metadata for {company='company', project='project'}"
  }

• New response:
  404

  {
  "message": "Unable to get Suite Metadata with suite name: test-suite, version: 999 for {company='company', project='project'}"
  }

6. Get locked suites
   http://aet-vagrant:8181/configs/locks

• Old response:

  {
  company-project-test-suite=company-project-test-suite-1548143700186, 
  secondcompany-secondproject-test-suite2=secondcompany-secondproject-test-suite2-1548143698893
  }

• New response:

  {
  "company-project-test-suite": "company-project-test-suite-1548141903906",
  "secondcompany-secondproject-test-suite2": "secondcompany-secondproject-test-suite2-1548141899754"
  }

Motivation and Context

Closes #425

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• I have reviewed (and updated if needed) the documentation regarding this change

---

I hereby agree to the terms of the AET Contributor License Agreement.

[Asia95]

this should be in unreleased section

[plutasnyy]

Is everything ok with formatting?

[wblachowski]

Looks fine to me, these are nested if statements. It's OK according to Google Style

[bambroziak]

Tested and accepted.
I've rebuilded Integration with changes and checked responses - all of them were new ones.

QA Covered.