Fix can_bloom to compare numbers.

Also adding a test suite, before we get proper infrastructure in place
just install mock and run the test_curator.py file.
Switched find_expired_indices to use datetimes and timedeltas

Also:
 - added tests
 - removed unused params
 - made time_unit and unit_count required params
Do not try and catch unrecoverable exceptions.

Especially when we are not catching them everywhere. Let the propagate
and the script fail.
Future proofing the use of the elasticsearch client.

No tests for now since we don't have integration tests yet