RDS service request validation

[sjones4]

RDS service request validation as per api.

Build: https://dev.azure.com/corymbia/eucalyptus/_build/results?buildId=1375 Test: https://dev.azure.com/corymbia/eucalyptus/_build/results?buildId=1376

Verified that existing manual rds tests pass with changes in place:

# euca-authorize -P tcp -p 5432 default
...
...
# euform-create-stack --template-file rds.yaml -p SecurityGroupId=sg-44fd450ab677ef6e3 -p SubnetId=subnet-72bee31afbbfcc9f6 rds-1
...
...
# aws rds describe-db-instances 
DBINSTANCES 1   False   cloud-1a    0   False   arn:aws:rds::000340531378:db/database-1 db.t2.small database-1  available   postgres    postgres    11  False   2021-06-22T05:18:36.529Z    username    False   False   True    False
DBSUBNETGROUP   arn:aws:rds::000340531378:subgrp/subnet-group-1 A subnet group description  subnet-group-1  Complete    vpc-547b1fdf520a27975
SUBNETS subnet-72bee31afbbfcc9f6    Active
SUBNETAVAILABILITYZONE  cloud-1a
ENDPOINT    database-1.s5afpqfhme5h.rds.qa64.eucalyptuscloud.net    5432
VPCSECURITYGROUPS   active  sg-44fd450ab677ef6e3
#
#
# podman run -it --rm docker.io/library/postgres:11-alpine psql -h database-1.s5afpqfhme5h.rds.qa64.eucalyptuscloud.net -U username postgres
^C

Password for user username: 
psql (11.12)
Type "help" for help.

postgres=# 
...

Relates to corymbia/eucalyptus#257