The default /etc/httpd/conf/httpd.conf file shipped by EL-6, contains
the line "Include conf.d/*.conf".  In EL-7, that line has been changed
to "IncludeOptional conf.d/*.conf", so it will not throw an error if
there are no files in the conf.d directory.  Change to handle both
variants, and also handle if there should be more than one such line,
or none at all.

The EL-7 httpd.conf file also contains "Include conf.modules.d/*.conf",
as they have moved all the default LoadModule directives to files in
the conf.modules.d directory.  We don't want to disable that, so keep
that line.

The conf.modules.d stuff also affects modules installed as separate
packages, e.g. mod_ssl, mod_wsgi and mod_perl, as the LoadModule
directive those packages provide are now in a separate file in the
conf.modules.d directory, not in the config file in conf.d.  That
only causes a warning about the module being loaded twice, though,
so is not particularly dangerous.