[boto_lambda] handle ommitted Permissions parameter

[ticosax]

What does this PR do?

If Permissions parameter was ommited but actual lambda function defines Permissions,
the state would fail attempting to compare old and new values.

An exception occurred in this state: Traceback (most recent call last):
File "/usr/lib/python2.7/dist-packages/salt/state.py", line 1703, in call
    **cdata['kwargs'])
File "/usr/lib/python2.7/dist-packages/salt/loader.py", line 1649, in wrapper
    return f(*args, **kwargs)
File "/usr/lib/python2.7/dist-packages/salt/states/boto_lambda.py", line 255, in function_present
    region, key, keyid, profile)
File "/usr/lib/python2.7/dist-packages/salt/states/boto_lambda.py", line 372, in _function_permissions_present
    diffs = salt.utils.compare_dicts(curr_permissions, Permissions)
File "/usr/lib/python2.7/dist-packages/salt/utils/__init__.py", line 2355, in compare_dicts
    elif key not in new:
TypeError: argument of type 'NoneType' is not iterable

What issues does this PR fix or reference?

none

Tests written?

Yes

[rallytime]

Thanks @ticosax! There is a little lint that needs to be cleaned up. Then we can get this in.

https://jenkins.saltstack.com/job/PR/job/salt-pr-lint-n/2500/violations/

[ticosax]

@rallytime Thanks. should be good now.