Attempt to fix name resolution (#4)

Option 3: Use resolvconf from core. Does not work as expected.
/sbin/resolvconf fails at execution with:
mkdir: cannot create directory '/run/resolvconf': Permission denied

snap/snapcraft.yaml

@@ -7,7 +7,7 @@ description: |
     the gateway and this process.
 license: GPL-3.0
 adopt-info: openfortivpn
-base: core18
+base: core
 confinement: strict
 grade: stable
 
@@ -17,10 +17,6 @@ architectures:
     - build-on: amd64
 
 layout:
-    /usr/sbin/pppd:
-        bind-file: $SNAP/usr/sbin/pppd
-    /sbin/resolvconf:
-        bind-file: $SNAP/sbin/resolvconf
     /etc/openfortivpn:
         bind: $SNAP_COMMON
 
@@ -45,20 +41,9 @@ parts:
             - pkg-config
             - libssl-dev
             - libsystemd-dev
-        stage-packages:
-            - ppp
-            - resolvconf
         stage:
             - bin/openfortivpn
-            - etc/network/*
-            - etc/ppp/*
-            - etc/resolvconf/*
-            - lib/resolvconf/list-records
-            - sbin/resolvconf
             - share/*
-            - usr/sbin/pppd
-            - usr/lib
-            - usr/share/ppp
         # Infer version from Git tags:
         # * Remove the leading "v" from openfortivpn Git tags.
         # * We propose specific Git tags for openfortivpn snaps, if needed.