rhel7stig: sshd.yml: Respect the STIG sshd configuration

Appending sshd configuration options at the end of the file doesn't work
as expected. If the same keyword is set multiple times, sshd will only
respect the first occurence. As such, all the options that we add at the
EOF will do nothing if any of them is already set in the file already.
In order to make sure that all our options are respected, we need to add
all of them at the beginning of the file. This can be easily
demonstrated if we use the following keywords in an sshd config file
assuming we have /etc/motd already.

PrintMotd yes
PrintMotd no

$ ssh root@localhost

Last login: Tue Oct 31 09:28:28 2017 from ::1
Have a lot of fun...

But if we swap the options to
PrintMotd no
PrintMotd yes

Last login: Tue Oct 31 09:29:55 2017 from ::1

Closes-Bug: #1728735
Change-Id: I02f2b9bc612d67ed7b23d853012d3b6374f65c9d

tasks/rhel7stig/sshd.yml

@@ -13,21 +13,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-# Adding additional sshd configuration options is usually easy, but if a
-# configuration file ends with certain configurations, like a "Match" stanza,
-# we need a blank line to separate those configurations from the ones that
-# are added by the security role. For that reason, we check for the existence
-# of a marker line here and add a marker line to the file if it doesn't exist.
-
-- name: Find first 'Match' line in sshd_config (if it exists)
-  shell: "grep '^Match' /etc/ssh/sshd_config || echo 'EOF'"
-  register: sshd_match_check
-  changed_when: False
-  check_mode: no
-  tags:
-    - always
-    - sshd
-
 - name: Copy login warning banner
   copy:
     content: "{{ security_login_banner_text }}"
@@ -45,7 +30,7 @@
     dest: /etc/ssh/sshd_config
     state: present
     marker: "# {mark} MANAGED BY ANSIBLE-HARDENING"
-    insertbefore: "{{ sshd_match_check.stdout_lines[0] }}"
+    insertbefore: "BOF"
     validate: '/usr/sbin/sshd -T -f %s'
     block: "{{ lookup('template', 'sshd_config_block.j2') }}"
   notify: