Added iam backend to servers, added some tests to check backend

moto/backends.py

@@ -8,6 +8,7 @@ from moto.ec2 import ec2_backend
 from moto.elb import elb_backend
 from moto.emr import emr_backend
 from moto.glacier import glacier_backend
+from moto.iam import iam_backend
 from moto.kinesis import kinesis_backend
 from moto.kms import kms_backend
 from moto.rds import rds_backend
@@ -29,6 +30,7 @@ BACKENDS = {
     'elb': elb_backend,
     'emr': emr_backend,
     'glacier': glacier_backend,
+    'iam': iam_backend,
     'kinesis': kinesis_backend,
     'kms': kms_backend,
     'redshift': redshift_backend,