[#2798] add http_host to engine analysis

[travisbgreen]

https://redmine.openinfosecfoundation.org/issues/2798

• [ x ] I have read the contributing guide lines at https://redmine.openinfosecfoundation.org/projects/suricata/wiki/Contributing
• [ x ] I have signed the Open Information Security Foundation contribution agreement at https://suricata-ids.org/about/contribution-agreement/
• [ x ] I have updated the user guide (in doc/userguide/) to reflect the changes made (if applicable)

Link to redmine ticket:

Describe changes:

• Added checks for host_header buffer

[victorjulien]

Code looks good. Would like to see a new version with an improved commit message. My suggestion would be something like:

engine-analysis: add support for http_host buffer

Add support for http_host buffer for more accurate reporting.

Bug: #2798

The subject line is : short description.

Minor other thing: the checkboxes should be fixed up. Removing the spaces does it.

Can you submit a new PR? Thanks!