Pause updates while purging or restarting apps, and ensure an applyTarget is triggered after the actions run

Signed-off-by: Pablo Carranza Velez <pablo@resin.io>

src/application-manager.coffee

@@ -61,10 +61,13 @@ class ApplicationManagerRouter
 					stoppedApp = _.cloneDeep(app)
 					stoppedApp.services = []
 					currentState.local.apps[appId] = stoppedApp
-					@deviceState.applyIntermediateTarget(currentState, { skipLock: true })
-					.then =>
-						currentState.local.apps[appId] = app
+					@deviceState.pausingApply =>
 						@deviceState.applyIntermediateTarget(currentState, { skipLock: true })
+						.then =>
+							currentState.local.apps[appId] = app
+							@deviceState.applyIntermediateTarget(currentState, { skipLock: true })
+					.finally =>
+						@deviceState.triggerApplyTarget()
 
 		doPurge = (appId, force) =>
 			@logger.logSystemMessage("Purging data for app #{appId}", { appId }, 'Purge data')
@@ -76,10 +79,13 @@ class ApplicationManagerRouter
 					purgedApp.services = []
 					purgedApp.volumes = {}
 					currentState.local.apps[appId] = purgedApp
-					@deviceState.applyIntermediateTarget(currentState, { skipLock: true })
-					.then =>
-						currentState.local.apps[appId] = app
+					@deviceState.pausingApply =>
 						@deviceState.applyIntermediateTarget(currentState, { skipLock: true })
+						.then =>
+							currentState.local.apps[appId] = app
+							@deviceState.applyIntermediateTarget(currentState, { skipLock: true })
+					.finally =>
+						@deviceState.triggerApplyTarget()
 			.tap =>
 				@logger.logSystemMessage('Purged data', { appId }, 'Purge data success')
 			.catch (err) =>

src/device-state.coffee

@@ -533,12 +533,26 @@ module.exports = class DeviceState extends EventEmitter
 				updateContext.applyContinueScheduled = false
 				@applyTarget({ force, initial, intermediate }, updateContext)
 
-	pauseNextApply: =>
-		@applyBlocker = new Promise (resolve) =>
-			@applyUnblocker = resolve
+	pausingApply: (fn) =>
+		lock = =>
+			@_writeLock('pause').disposer (release) ->
+				release()
+		pause = =>
+			Promise.try =>
+				res = null
+				@applyBlocker = new Promise (resolve) ->
+					res = resolve
+				return res
+			.disposer (resolve) ->
+				resolve()
+
+		Promise.using lock(), ->
+			Promise.using pause(), ->
+				fn()
 
 	resumeNextApply: =>
 		@applyUnblocker?()
+		return
 
 	triggerApplyTarget: ({ force = false, delay = 0, initial = false } = {}) =>
 		if @applyInProgress