Add constraints for names

We should make sure that environment names and application names adhere to naming constraints defined by the underlying cloud.

For instance, AWS RDS's name needs to be according to following constraints:

http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_Limits.html#RDS_Limits.Constraints

When creating a RDS instance for an environment, cloudark uses the name of the environment as the name of the RDS instance. So we need to adhere to the naming constraints of RDS when creating the environment otherwise we get errors like the following:

10/03/2017 09:28:06 PM Response body:

Sender
InvalidParameterValue
Invalid database identifier: 03oct2-2017-10-03-21-24-17

a8834b16-a8ab-11e7-88eb-53a6941873ad

10/03/2017 09:28:06 PM Event needs-retry.rds.CreateDBInstance: calling handler
10/03/2017 09:28:06 PM No retry needed.
10/03/2017 09:28:06 PM : create() /Users/vxk1803/kvr/repos/cloudark/server/server_plugins/aws/resource/rds_handler.py:25
10/03/2017 09:28:06 PM An error occurred (InvalidParameterValue) when calling the CreateDBInstance operation: Invalid database identifier: 03oct2-2017-10-03-21-24-17
Traceback (most recent call last):
File "/Users/vxk1803/kvr/repos/cloudark/server/server_plugins/aws/resource/rds_handler.py", line 80, in create
Tags=[{"Key":"Tag1", "Value":"Value1"}])