UI: checksum field is optional for direct-download templates on kvm

[weizhouapache]

Description

This PR fixes the UI issue that checksum field is required on UI.
this is a regression of #5151

Types of changes

• Breaking change (fix or feature that would cause existing functionality to change)
• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Enhancement (improves an existing feature and functionality)
• Cleanup (Code refactoring and cleanup, that may add test cases)

Feature/Enhancement Scale or Bug Severity

Feature/Enhancement Scale

• Major
• Minor

Bug Severity

• BLOCKER
• Critical
• Major
• Minor
• Trivial

Screenshots (if appropriate):

How Has This Been Tested?

[acs-robot]

Found UI changes, kicking a new UI QA build
@blueorangutan ui

[acs-robot]

Found Java/XML changes, kicking packaging job
@blueorangutan package

[acs-robot]

PR Coverage Report

CLASS	INSTRUCTION MISSED	INSTRUCTION COVERED	BRANCH MISSED	BRANCH COVERED	LINE MISSED	LINE COVERED
Volume	109	0	2	0	44	0
VolumeVO	529	133	4	0	179	39
VolumeObject	773	665	77	39	178	117
VmwareStorageProcessor	9892	9	940	0	2122	2
VolumeJoinDaoImpl	770	0	94	0	171	0
VolumeJoinVO	267	0	0	0	93	0
ConfigurationManagerImpl	18104	0	3032	0	3570	0
IpAddressManagerImpl	4045	0	461	0	806	0
ManagementServerImpl	11819	0	1052	0	2361	0
VolumeApiServiceImpl	10851	0	1500	0	2035	0
VirtualMachineMO	8953	135	1063	17	1982	31

[utchoang]

LGTM!