[AWS iam_policy] Avoid the _undefined name_ by catching the raised exception into the variable __e__ so it can be reported on the following line.
flake8 testing of https://github.com/ansible/ansible on Python 3.6.3
$ __flake8 . --count --select=E901,E999,F821,F822,F823 --show-source --statistics__
```
./lib/ansible/modules/cloud/amazon/iam_policy.py:305:16: F821 undefined name 'e'
if e.errno == 2:
^
./lib/ansible/modules/cloud/misc/rhevm.py:594:24: F821 undefined name 'e'
setMsg(str(e))
^
./lib/ansible/modules/files/archive.py:391:92: F821 undefined name 'e'
module.fail_json(dest=dest, msg='Error deleting some source files: ' + str(e), files=errors)
^
3 F821 undefined name 'e'
3
```
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