Fix state and pillar targeting for numbered masters

We now number the servo-master IDs like other machines,
so use PCRE targeting to match the `servo-master\d+` pattern
for both states and the Travis test pillars.

This ensures the relevant pillars are available to master machines
and the master-specific states are applied.

.travis/test_pillars/top.sls

@@ -3,7 +3,8 @@ base:
     - travis
     - buildbot.common
 
-  'servo-master':
+  'servo-master\d+':
+    - match: pcre
     - buildbot.master
     - homu
 

top.sls

@@ -30,6 +30,7 @@ base:
     - xvfb
 
   'servo-master\d+':
+    - match: pcre
     - git
     - buildbot.master
     - homu