Add MinGW 4.9.1 to Windows 7 CI - and Packaging nodes

This will install MinGW 4.9.1 i686 posix dwarf to x86 nodes and MinGW
4.9.1 x86_64 posix seh to x64 nodes

Change-Id: I00da44251efe6f87587594e683e1e0b6dd0e18d5
Reviewed-by: Tony Sarajärvi <tony.sarajarvi@digia.com>