Description of problem:
Python module rhsm is used by other projects (e.g. virt-who) and it should not call exit(), but it should raise some exception, because application using rhsm module cannot resurrect from calling exit() by some external module.

Version-Release number of selected component (if applicable):
# subscription-manager version
server type: Red Hat Subscription Management
subscription management server: 2.0.37-1
subscription management rules: 5.24.1
subscription-manager: 1.19.12-1.el7
python-rhsm: 1.19.6-1.el7

How reproducible:
always


Steps to Reproduce:
1. Start Python interpreter:

$ python

2. Import rhsm submodule called 'certificate'

>>> import python_rhsm.certificate

3. Try to get certificate from some non-existent file:

>>> c = python_rhsm.certificate.create_from_file('/foo/non_existing_cert.pem')
No such file or directory

Actual results:
Python interpreter is terminated as well any other program trying to do similar thing.

Expected results:
Calling python_rhsm.certificate.create_from_file('/foo/non_existing_cert.pem') should raise some exception.

Additional info:
This can happen in production, when system is not registered and there is no file: /etc/pki/consumer/cert.pem. There are no other exit() call in rhsm module only one in: python-rhsm/src/rhsm/certificate2.py