Ignore failures when loading nf_conntrack_proto_sctp kernel module

Ignore failures when loading nf_conntrack_proto_sctp kernel module

Ignore failures if nf_conntrack_proto_sctp module failed to load.
Since RHEL 7.4, nf_conntrack_proto_sctp module is compiled into the
kernel instead of as a module as the sctp support.
TripleO will still try to load the module to support RHEL 7.3, but
in the future will remove the module management and rely on the kernel
provided in newer versions of RHEL.

Co-Authored-By: Or Idgar <oidgar@redhat.com>
Co-Authored-By: Alex Schultz <aschultz@redhat.com>
Co-Authored-By: Emilien Macchi <emilien@redhat.com>
Change-Id: I8f1c841a7c0f3b1247aba2b959b6dfbe43d8cd79
Closes-Bug: 1695885