Change error computation on JSON Unmarshal and create subtests on table test scenarios

[jonathanbeber]

Change error computation on JSON Unmarshall

The Unmarshall function on the encoding/JSON default library returns
different errors for different go versions. On Go 1.12, the version used
currently on the CI system it returns json: cannot unmarshal number into Go struct field PostgresSpec.teamId of type string. On Go 1.13.5 it
returns json: cannot unmarshal number into Go struct field PostgresSpec.spec.teamId of type string. The new version includes more
details of the whole structure being unmarshalled.

This commit introduces the same error but one level deeper on the JSON
structure. It creates consistency across different Go versions.

---

Create subtests on table test scenarios

The Run method of T allows defining subtests creating hierarchical tests.
It provides better visibility of tests in case of failure. More
details on https://golang.org/pkg/testing/.

This commit converts each test scenario on
pkg/apis/acid.zalan.do/v1/util_test.go to subtests, providing a better
visibility and the debugging environment when working with tests. The
following code snippet shows a error during test execution with
subtests:

--- FAIL: TestUnmarshalMaintenanceWindow (0.00s)
    --- FAIL: TestUnmarshalMaintenanceWindow/expect_error_as_'From'_is_later_than_'To' (0.00s)

It included a about field on test scenarios describing the test
purpose and/or it expected output. When a description was provided with
comments it was moved to the about field.

[jonathanbeber]

For reviewers, I recommend the diff view without empty spaces

[jonathanbeber]

On CI it has a better test description as well:

--- PASS: TestClusterName (0.00s)
    --- PASS: TestClusterName/common_team_and_cluster_name (0.00s)
    --- PASS: TestClusterName/cluster_name_with_hyphen (0.00s)
    --- PASS: TestClusterName/cluster_and_team_name_with_hyphen (0.00s)
    --- PASS: TestClusterName/expect_error_as_cluster_name_is_just_hyphens (0.00s)
    --- PASS: TestClusterName/expect_error_as_cluster_name_is_too_long (0.00s)
    --- PASS: TestClusterName/expect_error_as_cluster_name_does_not_match_{TEAM}-{NAME}_format (0.00s)
    --- PASS: TestClusterName/expect_error_as_team_and_cluster_name_are_empty (0.00s)
    --- PASS: TestClusterName/expect_error_as_cluster_name_is_empty_and_team_name_is_a_hyphen (0.00s)
    --- PASS: TestClusterName/expect_error_as_cluster_name_is_empty,_team_name_is_a_hyphen_and_cluster_name_is_empty (0.00s)
    --- PASS: TestClusterName/expect_error_as_cluster_and_team_name_are_hyphens (0.00s)

[FxKu]

Thanks for this contribution. Works also with my Go 1.12 so 👍
At some point we should make our other tests also more wordy.

[FxKu]

👍

[Jan-M]

👍