Add Snapcraft metadata and install/maintenance hooks (#666)

* Add Snapcraft metadata and install/maintenance hooks

* Move set-environment script into snap/local

* snap: Remove diesel-cli part.

This *was* necessary as of 0.3.0, but now `plm migrations run` does the job.

* snap: Add an actual description

* snap: Add an 'enabled' config item.

Don't try to run until enabled is set, and automatically run the
migrations when we are enabled

snap/hooks/configure

@@ -0,0 +1,48 @@
+#!/bin/sh
+
+db_type="$(snapctl get db.type)"
+db_url="$(snapctl get db.url)"
+if [ "${db_type}" = "sqlite" ]
+then
+    if [ -n "${db_url}" ]
+    then
+        echo "sqlite backend does not use db.url key"
+        exit 1
+    fi
+elif [ "${db_type}" = "postgres" ]
+then
+    if [ -z "${db_url}" ]
+    then
+        echo "postgres backend requires db.url to be set"
+        exit 1
+    fi
+elif [ -n "${db_type}" ]
+then
+    echo "Invalid db.type: " ${db_type}
+    exit 1
+fi
+
+base_url="$(snapctl get base-url)"
+enabled="$(snapctl get enabled)"
+
+if [ -n ${enabled} -a \( "${enabled}" != "true" -a "${enabled}" != "false" \) ]
+then
+    echo "Invalid 'enabled' setting: ${enabled}. Valid values are 'true' or 'false'"
+    exit 1
+fi
+
+if [ -n ${base_url} -a \( -z "${enabled}" -o "${enabled}" = "false" \) ]
+then
+    echo "All required configuration available."
+    echo "Plume can now be enabled by setting 'snap set plume enabled=true' and restarting the service \
+with 'snap restart plume'"
+fi
+
+if [ "${enabled}" = "true" -a ! -e ${SNAP_COMMON}/initial-migrations-run ]
+then
+    cd ${SNAP}
+    exec ./set-environment bin/plm migration run --path ${SNAP_DATA}
+    touch ${SNAP_COMMON}/initial-migrations-run
+fi
+
+exit 0

snap/hooks/install

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+openssl rand -base64 32 > ${SNAP_COMMON}/rocket-secret-key

snap/hooks/post-refresh

@@ -0,0 +1,11 @@
+#!/bin/sh
+
+db_type=$(snapctl get db.type)
+
+if [ -z "${db_type}" ]
+then
+    exit 0
+fi
+
+cd ${SNAP}
+exec ./set-environment bin/plm migration run --path ${SNAP_DATA}