BaseTools/GenFds: cleanup GenFds

1) remove wildcard imports and use explicit imports
2) refactor to use shared variables from Common/DataType
3) rename to not shadow imports
4) don't assign a variable in a loop (just do final assignment)
5) remove spaces, parens, unused or commented out code, etc.
6) merge unnecessary parent classes into child
7) refactor to share DXE and PEI apriori GUIDs from one place
  this includes changes to Build and EOT files
8) for PEP8, dont use __ for custom methods.

Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Bob C Feng <bob.c.feng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>

BaseTools/Source/Python/build/BuildReport.py

@@ -46,6 +46,7 @@ from Common.StringUtils import NormPath
 from Common.DataType import *
 import collections
 from Common.Expression import *
+from GenFds.AprioriSection import DXE_APRIORI_GUID, PEI_APRIORI_GUID
 
 ## Pattern to extract contents in EDK DXS files
 gDxsDependencyPattern = re.compile(r"DEPENDENCY_START(.+)DEPENDENCY_END", re.DOTALL)
@@ -1873,8 +1874,8 @@ class FdRegionReport(object):
         #
         # Add PEI and DXE a priori files GUIDs defined in PI specification.
         #
-        self._GuidsDb["1B45CC0A-156A-428A-AF62-49864DA0E6E6"] = "PEI Apriori"
-        self._GuidsDb["FC510EE7-FFDC-11D4-BD41-0080C73C8881"] = "DXE Apriori"
+        self._GuidsDb[PEI_APRIORI_GUID] = "PEI Apriori"
+        self._GuidsDb[DXE_APRIORI_GUID] = "DXE Apriori"
         #
         # Add ACPI table storage file
         #