BaseTools/Capsule: Prevent traceback during signing operations

BaseTools/Capsule: Prevent traceback during signing operations

https://bugzilla.tianocore.org/show_bug.cgi?id=1046
https://bugzilla.tianocore.org/show_bug.cgi?id=1048
https://bugzilla.tianocore.org/show_bug.cgi?id=1050

Remove raise statements that generate Tracebacks that were only
intended for development/debug.  With the raise statements removed
proper error messages are shown.

Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>