The Parser 'RHSMConf ' should set allow_no_value to "True" when parse_content

[shzhou12]

According to the docstring example, The parser should allow no value when parse_content:
https://github.com/RedHatInsights/insights-core/blob/master/insights/parsers/rhsm_conf.py#L39

Typical content of "/etc/rhsm/rhsm.conf" is::

    # Unified Entitlement Platform Configuration
    [server]
    # Server hostname:
    hostname = subscription.rhn.redhat.com

    # Server prefix:
    prefix = /subscription

    # Server port:
    port = 443

    # Set to 1 to disable certificate validation:
    insecure = 0

    # Set the depth of certs which should be checked
    # when validating a certificate
    ssl_verify_depth = 3

    # an http proxy server to use
    proxy_hostname =

    # port for http proxy server
    proxy_port =