support iam role for cloud services and agencies

[ShiChangkuo]

What this PR does / why we need it:

Which issue this PR fixes:
(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged)
fixes #1289

Special notes for your reviewer:

Release note:

PR Checklist

• Tests added/passed.
• Documentation updated.
• Schema updated.

Acceptance Steps Performed

$ make testacc TEST='./huaweicloud' TESTARGS='-run TestAccIdentityRole'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./huaweicloud -v -run TestAccIdentityRole -timeout 360m -parallel 4
=== RUN   TestAccIdentityRoleDataSource_basic
=== PAUSE TestAccIdentityRoleDataSource_basic
=== RUN   TestAccIdentityRole_basic
=== PAUSE TestAccIdentityRole_basic
=== RUN   TestAccIdentityRole_agency
=== PAUSE TestAccIdentityRole_agency
=== CONT  TestAccIdentityRoleDataSource_basic
=== CONT  TestAccIdentityRole_agency
=== CONT  TestAccIdentityRole_basic
--- PASS: TestAccIdentityRole_agency (10.72s)
--- PASS: TestAccIdentityRoleDataSource_basic (14.28s)
--- PASS: TestAccIdentityRole_basic (16.59s)
PASS
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud       16.650s