Handle the case where include_pattern and exclude_pattern exist but are empty strings

##### Issue Type:

Bugfix Pull Request

##### Ansible Version:

ansible 1.8 (devel ab6e1a43e9) last updated 2014/08/12 15:38:36 (GMT -400)

##### Environment:

Fedora 20 and CentOS 6.5

##### Summary:

Blank values for include_pattern or exclude_pattern in ec2.ini results in a traceback.

##### Steps To Reproduce:

Create an ec2.ini config with include_pattern or exclude_pattern in the file, but containing empty strings then using the ec2.py inventory will result in the following traceback:

Traceback (most recent call last):
  File "/etc/ansible/hosts", line 711, in <module>
    Ec2Inventory()
  File "/etc/ansible/hosts", line 156, in __init__
    self.do_api_calls_update_cache()
  File "/etc/ansible/hosts", line 302, in do_api_calls_update_cache
    self.get_instances_by_region(region)
  File "/etc/ansible/hosts", line 329, in get_instances_by_region
    self.add_instance(instance, region)
  File "/etc/ansible/hosts", line 395, in add_instance
    if self.pattern_include and not self.pattern_include.match(dest):
AttributeError: 'Ec2Inventory' object has no attribute 'pattern_include'

##### Expected Results:

Should treat empty strings the same as not having those options in the file.

##### Actual Results:

Throws the above traceback.