MdeModulePkg/CapsuleApp: Enhance Capsule-On-Disk related functions.

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1840

1. Introduce an internal header file to put definitions in it.
2. Add missing '\n' in usage.
3. Fix the dead loop of CapsuleApp -L.
4. Fix the bug that CapsuleApp -OD cannot perform capsules in sub-
folder.
5. Optimize the handling for option -NR and -OD to support both
'CapsuleApp <Capsule> -OD -NR' and 'CapsuleApp <Capsule> -NR -OD'.
6. Check if Capsule-On-Disk is supported by "OsIndicationsSupported"
variable firstly before processing capsules. If not supported, prompt
an error message and quit the process.

Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Chao B Zhang <chao.b.zhang@intel.com>
Signed-off-by: Wei6 Xu <wei6.xu@intel.com>
Reviewed-by: Chao B Zhang <chao.b.zhang@intel.com>
Acked-by: Hao A Wu <hao.a.wu@intel.com>

MdeModulePkg/Application/CapsuleApp/CapsuleApp.inf

@@ -4,7 +4,7 @@
 # This application can trigger capsule update process. It can also
 # generate capsule image, or dump capsule variable information.
 #
-#  Copyright (c) 2016 - 2018, Intel Corporation. All rights reserved.<BR>
+#  Copyright (c) 2016 - 2019, Intel Corporation. All rights reserved.<BR>
 #  SPDX-License-Identifier: BSD-2-Clause-Patent
 #
 ##
@@ -26,6 +26,7 @@
 
 [Sources]
   CapsuleApp.c
+  CapsuleApp.h
   CapsuleDump.c
   CapsuleOnDisk.c
   AppSupport.c