ATLAS-5352 :- Add Unit Testcases for Relationship

[nixonrodrigues]

What changes were proposed in this pull request?

Added Unit testcase for for Relationship read API.

How was this patch tested?

The UT were executed in local with mvn command to

mvn test -pl repository,webapp \
  -Dtest=org.apache.atlas.repository.store.graph.v2.AtlasRelationshipStoreV2ReadAuthTest,org.apache.atlas.web.rest.SearchDownloadFileValidatorTest \
  -DfailIfNoTests=false

[INFO] -------------------------------------------------------
[INFO]  T E S T S
[INFO] -------------------------------------------------------
[INFO] Running org.apache.atlas.repository.store.graph.v2.AtlasRelationshipStoreV2ReadAuthTest
[INFO] Tests run: 6, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 1.722 s -- in org.apache.atlas.repository.store.graph.v2.AtlasRelationshipStoreV2ReadAuthTest
[INFO] 
[INFO] Results:
[INFO] 
[INFO] Tests run: 6, Failures: 0, Errors: 0, Skipped: 0

[INFO]  T E S T S
[INFO] -------------------------------------------------------
[INFO] Running org.apache.atlas.web.rest.SearchDownloadFileValidatorTest
[INFO] Tests run: 9, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.312 s -- in org.apache.atlas.web.rest.SearchDownloadFileValidatorTest
[INFO] 
[INFO] Results:
[INFO] 
[INFO] Tests run: 9, Failures: 0, Errors: 0, Skipped: 0
[INFO] 
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary for Apache Atlas Repository 3.0.0-SNAPSHOT:
[INFO] 
[INFO] Apache Atlas Repository ............................ SUCCESS [  7.418 s]
[INFO] Apache Atlas Web Application ....................... SUCCESS [ 26.678 s]