kops: kops can't assume roles in ~/.aws/config profiles by default

Not sure this is a documentation issue, a small bug, or even a feature request:

By default, kops will not assume roles defined in profiles in ~/.aws/config. Golang’s AWS SDK says that by defining the environment variable AWS_SDK_LOAD_CONFIG, the sessions will be created with the ability to assume roles, set default regions.

I don’t quite understand the reason Golang SDK devs decided to go this route, but folks used to CLI/boto will find the current behavior weird, and will likely file bugs or ask questions in Slack.

#### using a profile that the user assumes a role
# export AWS_PROFILE=subaccount-profile-with-role

# aws ec2 describe-availability-zones --output text
AVAILABILITYZONES       us-west-2       available       us-west-2a
AVAILABILITYZONES       us-west-2       available       us-west-2b
AVAILABILITYZONES       us-west-2       available       us-west-2c

# kops create -f /tmp/my-config --state --state s3://my-bucket/subfolder/kops   ## doesn't work
error: error populating configuration: Got an error while querying for valid regions (verify your AWS credentials?)

# export AWS_SDK_LOAD_CONFIG=1

# kops create -f /tmp/my-config --state --state s3://my-bucket/subfolder/kops  ## works!



#### using a profile that has access keys associated with the user
# export AWS_PROFILE=subaccount-profile-with-access-keys

# kops create -f /tmp/my-config --state --state s3://my-bucket/subfolder/kops   ## works!