Enable jar verification in VMR signing validation

[ellahathaway]

See #4929 (comment)

Jar verification in SignCheck currently fails to find the hash algorithm of signed jar files: <File Name="signalr-<version>-javadoc.jar" Outcome="Unsigned" Error="Unsupported hash algorithm name&#xD;&#xA;Parameter name: hashName" />. This is preventing us from enabling jar verification in the VMR signing validation.

Two items should be completed as part of this issue:

1. Fix jar verification in SignCheck
2. Enable jar verification in the VMR signing validation