Add validations to AWS EC2 autoload

[alonagetzler]

currently the Autoload that comes with the AWS EC2 doesn't do anything (mock), we need to align with the vCenter cloud provider and do some basic validations on the inputs given by the user (that we actually find the VPC, SG, S3 bucket etc.)

[alexazarh]

As a user I want to get feedback from the portal when I input data into attributes to know if the data is valid.

We need to do the following validations:

1. REGION - validate region value is valid by creation the clients successfully
2. KEYPAIRS LOCATION - validate bucket with this name exist in S3
3. AWS MGMT VPC ID - validate vpc exists in selected region
4. AWS MGMT SG ID - validate SG exists in Mgmt VPC
5. MAX STORAGE SIZE & MAX STORAGE IOPS - validate its a zero or postive int
6. INSTANCE TYPE - validate value is legal in aws
7. NETWORKS IN USE - if Mgmt VPC cidr doesnt exist in this attribute than we need to add it in the problematically.

[TomerAdmon]

add error handling for Successfully connecting to AWS API