[RDS] Fix template application

[outcatcher]

Summary of the Pull Request

Re-apply templates with auto-reset parameters (e.g max_connections)

Restart RDS instance after re-apply if required

Minor style fixes

Fix template values in the test

Fix #934

PR Checklist

• Refers to: [RDSv3] Adding param_group_id to RDS instance does not seem to work #934
• Tests added/passed.

Acceptance Steps Performed

=== RUN   TestAccRdsInstanceV3Basic
--- PASS: TestAccRdsInstanceV3Basic (1111.24s)
=== RUN   TestAccRdsInstanceV3ElasticIP
--- PASS: TestAccRdsInstanceV3ElasticIP (683.56s)
=== RUN   TestAccRdsInstanceV3HA
    resource_opentelekomcloud_rds_instance_v3_test.go:93: OS_AVAILABILITY_ZONE_2 is empty
--- SKIP: TestAccRdsInstanceV3HA (0.00s)

Test ignored.
=== RUN   TestAccRdsInstanceV3OptionalParams
--- PASS: TestAccRdsInstanceV3OptionalParams (658.45s)
=== RUN   TestAccRdsInstanceV3Backup
--- PASS: TestAccRdsInstanceV3Backup (689.72s)
=== RUN   TestAccRdsInstanceV3TemplateConfig
restart Rds instance body =  map[restart:{}]
--- PASS: TestAccRdsInstanceV3TemplateConfig (716.29s)
=== RUN   TestAccRdsInstanceV3InvalidDBVersion
--- PASS: TestAccRdsInstanceV3InvalidDBVersion (1.86s)
PASS

Process finished with the exit code 0

[otc-zuul]

Build succeeded.

• golang-make-test : SUCCESS in 3m 32s
• golang-make-vet : SUCCESS in 8m 44s
• goreleaser-build : SUCCESS in 8m 27s