fix: allow use of built-in routing tables

Cause: The user is trying to specify the routing table to use by the name of
a built-in routing table defined in /usr/share/iproute2/rt_tables such as `main`.

Consequence: The network role gives an error:
"cannot find route table main in `/etc/iproute2/rt_tables` or `/etc/iproute2/rt_tables.d/`"
The workaround is that the user must specify the table by number instead of name e.g
`table: 254` instead of `table: main`

Fix: Look for table mappings in /usr/share/iproute2/rt_tables as well as the other
paths.

Result: The user can use built-in route table names.

Signed-off-by: Rich Megginson <rmeggins@redhat.com>

tests/playbooks/tests_route_table.yml

@@ -49,6 +49,11 @@
                   metric: 50
                   table: 30200
                   src: 198.51.100.3
+                - network: 198.51.101.128
+                  prefix: 26
+                  gateway: 198.51.101.1
+                  metric: 2
+                  table: main
 
     - name: Get the routes from the route table 30200
       command: ip route show table 30200
@@ -62,6 +67,12 @@
       ignore_errors: true
       changed_when: false
 
+    - name: Get the routes from the route table main
+      command: ip route show table main
+      register: route_table_main
+      ignore_errors: true
+      changed_when: false
+
     - name: Assert that the route table 30200 contains the specified route
       assert:
         that:
@@ -81,6 +92,14 @@
         msg: "the route table 30400 does not exist or does not contain the
           specified route"
 
+    - name: Assert that the route table main contains the specified route
+      assert:
+        that:
+          - route_table_main.stdout is search("198.51.101.128/26 via
+            198.51.101.1 dev ethtest0 proto static metric 2")
+        msg: "the route table main does not exist or does not contain the
+          specified route"
+
     - name: Create a dedicated test file in `/etc/iproute2/rt_tables.d/` and
             add a new routing table
       lineinfile:
@@ -121,6 +140,11 @@
                   metric: 50
                   table: custom
                   src: 198.51.100.3
+                - network: 198.51.101.128
+                  prefix: 26
+                  gateway: 198.51.101.1
+                  metric: 2
+                  table: custom
 
     - name: Get the routes from the named route table 'custom'
       command: ip route show table custom
@@ -139,6 +163,8 @@
           - route_table_custom.stdout is search("192.0.2.64/26 via
             198.51.100.8 dev ethtest0 proto static src 198.51.100.3
             metric 50")
+          - route_table_custom.stdout is search("198.51.101.128/26 via
+            198.51.101.1 dev ethtest0 proto static metric 2")
         msg: "the named route table 'custom' does not exist or does not contain
           the specified route"