Changes the ApplicationEventHandler to check if the db is configured instead of being connected to which can cause issues if SQLCE file is locked by another app domain on startup. Then we verify in the CoreBootManager that the db can be connected to with a retry policy. Changes the db context CanConnect method to not store a static value since it might later be able to be connected to.

src/Umbraco.Core/Exceptions/UmbracoStartupFailedException.cs

@@ -0,0 +1,18 @@
+using System;
+
+namespace Umbraco.Core.Exceptions
+{
+    /// <summary>
+    /// An exception that is thrown if the umbraco application cannnot boot
+    /// </summary>
+    public class UmbracoStartupFailedException : Exception
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="T:System.Exception"/> class with a specified error message.
+        /// </summary>
+        /// <param name="message">The message that describes the error. </param>
+        public UmbracoStartupFailedException(string message) : base(message)
+        {
+        }
+    }
+}