Make use of local polkit.its

Drop the policykit-1 build-dep for Ubuntu, and make
instead use of a copy of polkit.its in the source which
will be available to all distros.

packaging/ubuntu-16.04/control

@@ -29,7 +29,6 @@ Build-Depends: autoconf,
                libudev-dev,
                openssh-client,
                pkg-config,
-               policykit-1,
                python3,
                python3-docutils,
                python3-markdown,

po/its/polkit.its

@@ -0,0 +1,8 @@
+<?xml version="1.0"?>
+<its:rules xmlns:its="http://www.w3.org/2005/11/its"
+           version="2.0">
+  <its:translateRule selector="//*" translate="no"/>
+  <its:translateRule selector="//action/description |
+                               //action/message"
+                     translate="yes"/>
+</its:rules>

update-pot

@@ -26,6 +26,7 @@ find "$HERE" -name "*.go" -type f -print0 | xargs -0 \
 
 xgettext "$HERE"/data/polkit/*.policy \
     -o "$OUTPUT" \
+    --its="$HERE/po/its/polkit.its" \
     --no-location \
     --package-name=snappy \
     --msgid-bugs-address=snappy-devel@lists.ubuntu.com \