Description of problem:
When there is a malformed custom fact or simply an empty custom facts file, a traceback occurs during registration.

This is a regression from RHEL7.3 where a WARNING like the following was written to rhsm.log

[WARNING]  @facts.py:125 - Unable to load custom facts file: /etc/rhsm/facts/empty.facts



Version-Release number of selected component (if applicable):
[root@jsefler-rhel7 ~]# rpm -q subscription-manager python-rhsm
subscription-manager-1.19.4-1.el7.x86_64
python-rhsm-1.19.2-1.el7.x86_64


How reproducible:


Steps to Reproduce:
[root@jsefler-rhel7 ~]# touch /etc/rhsm/facts/empty.facts
[root@jsefler-rhel7 ~]# subscription-manager register
Registering to: jsefler-candlepin.usersys.redhat.com:8443/candlepin
Username: testuser1
Password: 
com.redhat.RHSM1.Error: Traceback (most recent call last):
  File "/usr/lib64/python2.7/site-packages/dbus/service.py", line 707, in _message_cb
    retval = candidate_method(self, *args, **keywords)
  File "<string>", line 2, in GetFacts
  File "/usr/lib/python2.7/site-packages/rhsmlib/dbus/util.py", line 32, in dbus_handle_exceptions
    ret = func(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/rhsmlib/dbus/facts/base.py", line 79, in GetFacts
    results.update(fact_collector.GetFacts())
  File "<string>", line 2, in GetFacts
  File "/usr/lib/python2.7/site-packages/rhsmlib/dbus/util.py", line 32, in dbus_handle_exceptions
    ret = func(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/rhsmlib/dbus/facts/base.py", line 43, in GetFacts
    collection = self.facts_collector.collect()
  File "/usr/lib/python2.7/site-packages/rhsmlib/facts/collector.py", line 84, in collect
    facts_dict.update(self.get_all())
  File "/usr/lib/python2.7/site-packages/rhsmlib/facts/host_collector.py", line 85, in get_all
    custom_facts_dict = custom_facts.get_all()
  File "/usr/lib/python2.7/site-packages/rhsmlib/facts/custom.py", line 111, in get_all
    for custom_facts in facts_dir:
  File "/usr/lib/python2.7/site-packages/rhsmlib/facts/custom.py", line 85, in __iter__
    yield CustomFacts.from_json(fact_file.read())
  File "/usr/lib/python2.7/site-packages/rhsmlib/facts/custom.py", line 37, in from_json
    custom_facts.data = data
RHSM1DBusException: com.redhat.RHSM1.Error: UnboundLocalError: local variable 'data' referenced before assignment


Actual results:
 above

Expected results:
 expected a successful register with the following rhsm.log entry
 [WARNING]  @facts.py:125 - Unable to load custom facts file: /etc/rhsm/facts/empty.facts



Additional info:

The same traceback is thrown when a custom facts file has malformed json, like this...
[root@jsefler-rhel7 ~]# cat /etc/rhsm/facts/malformed.facts
{"malformed_fact":"value" is "misquoted"}