fix error when running in non us_east_1 region

When trying to execute Lab 4.1 (IAM Role) in a region different from US_EAST_1, Lab execution fails with :
```
Caught an AmazonServiceException, which means your request made it AWS,
but was rejected with an error response for some reason.
Error Message: Status Code: 403, AWS Service: AmazonIdentityManagement, AWS Request ID: a563dbd8-77a9-11e3-8125-51be2e0317da, AWS Error Code: SignatureDoesNotMatch, AWS Error Message: Credential should be scoped to a valid region, not 'eu-west-1'.
HTTP Status Code: 403
AWS Error Code: SignatureDoesNotMatch
Error Type: Client
Request ID: a563dbd8-77a9-11e3-8125-51be2e0317da
Stack trace:
[Ljava.lang.StackTraceElement;@7d0d60e4
```
###Cause :
IAM request must be scoped to US_EAST_1, even if the rest of the lab is executed in another region.
http://docs.aws.amazon.com/general/latest/gr/signature-v4-troubleshooting.html

###How to change region :
Change line 47 in Lab41.java
Error occurs at line 127 in SolutionCode.java

This commit (https://github.com/sebsto/devonaws-labs-java/commit/23c6fec74494f110d0bb19a399e09c2451db3959)  fixes this issue