Hammer CLI

Cloned from https://bugzilla.redhat.com/show_bug.cgi?id=1281346

Description of problem:
hammer host create --help page should include more details with reference to the network interfaces specifications.

Version-Release number of selected component (if applicable):
hammer 0.7.0
hammer_cli_foreman 0.7.0

Issue :
hammer host create --help page should include more details with reference to the network interfaces specifications.

For example help with creation of virtual interfaces in VM creation in libvirt

Actual results:
Current help page outputs

#  hammer host create --help

 --interface INTERFACE                                  Interface parameters.
                                                        Comma-separated list of key=value.
                                                        Can be specified multiple times.

Expected results:
We should have something similar as detailed in https://github.com/theforeman/hammer-cli-foreman/blob/master/doc/host_create.md or https://gist.github.com/tstrachota/f7858388976f19317b73