BreadcrumbStore require concurrency lock

[pranavkm]

From the CI:

System.IO.IOException: The process cannot access the file 'C:\ProgramData\Microsoft DNX\BreadcrumbStore\Microsoft.Framework.WebEncoders.Core.1.0.0-beta5-11433' because it is being used by another process.
at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize)
at Microsoft.Framework.Runtime.Servicing.Breadcrumbs.CreateBreadcrumbFile(String fileName)
at Microsoft.Framework.Runtime.Servicing.Breadcrumbs.WriteAllBreadcrumbsInternal()
at Microsoft.Framework.Runtime.Servicing.Breadcrumbs.<WriteAllBreadcrumbs>b__13_0(Object _)
at System.Threading.QueueUserWorkItemCallback.WaitCallback_Context(Object state)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
at System.Threading.ThreadPoolWorkQueue.Dispatch()

[moozzyk]

Dupe of #1733