CA-229031: improve error handling
CA-229031: improve error handling

Catch keyfiles that have multiple keys present, terminate when usage
is displayed.

Signed-off-by: Simon Rowe <6b0999b796d5e18833f96f31b20ec46c7a765474@eu.citrix.com>

Frezzle/xen-api,Frezzle/xen-api,thomassa/xen-api,euanh/xen-api,thomassa/xen-api,euanh/xen-api,euanh/xen-api,euanh/xen-api,thomassa/xen-api,Frezzle/xen-api,thomassa/xen-api,srowe/xen-api,srowe/xen-api,srowe/xen-api,Frezzle/xen-api,thomassa/xen-api,thomassa/xen-api,Frezzle/xen-api,srowe/xen-api,euanh/xen-api,srowe/xen-api,euanh/xen-api