gardenctl ssh <aws_node> fails with InvalidParameterValue

[dansible]

Describe the bug
gardenctl ssh <aws_node> fails with InvalidParameterValue (using gardenctl/gctl-aws cluster)

To Reproduce
Using 52235f2 with a test cluster gives:

$ go run cmd/gardenctl/main.go ssh ip-XXXX.eu-west-1.compute.internal 

Warning:
Be aware that you are entering an untrusted environment!
Do not enter credentials or sensitive data within the ssh session that cluster owners should not have access to.

Downloaded id_rsa key
Check Public IP

(1/4) Fetching data from target shoot cluster
Data fetched from target shoot cluster.

(2/4) Setting up bastion host security group
Security Group exists sg-0f4274271179c8402 skipping creation.

(3/4) Creating bastion host and node host security group
Bastion Host exists, skipping creation.
2020/11/13 10:16:47 AWS CLI failed with
An error occurred (InvalidParameterValue) when calling the AuthorizeSecurityGroupIngress operation: CIDR block /32 is malformed

exit status 254
exit status 1

Using just the nostname:

$ go run cmd/gardenctl/main.go ssh ip-XXXX

Warning:
Be aware that you are entering an untrusted environment!
Do not enter credentials or sensitive data within the ssh session that cluster owners should not have access to.

Downloaded id_rsa key
Check Public IP

(1/4) Fetching data from target shoot cluster
2020/11/13 09:25:29 AWS CLI failed with
An error occurred (InvalidParameterValue) when calling the DescribeSecurityGroups operation: vpc-id

exit status 254
exit status 1

Gardenctl Version (please complete the following information):

• Version/Commit 52235f2

[neo-liang-sap]

/assign

[neo-liang-sap]

Hi @dansible , i was unable to reproduce your problem but i found some issue in current ssh_aws.go
i submitted a PR #446 , i added some detailed information why i propose this PR in #446 , please review it when you have time.

BTW i upgraded my aws in local and here's my version

aws --version                                              (ccee-m3/default)
aws-cli/2.1.1 Python/3.7.4 Darwin/19.6.0 exe/x86_64

Thanks!
-Neo