Fix NullPointerException when disabling and reenabling SSL

[torusrxxx]

Setting keyStore to null will result in NullPointerException when SSL is reenabled and loadKeyStoreAndCreateCertificate is executed. Load a null key store instead.
Avoid adding strict-transport-security header twice. The second addition of strict-transport-security header does not check whether fproxy SSL is enabled because container is not a static member. As a result, strict-transport-security header is sent when SSL is enabled but fproxy SSL is disabled.

[ArneBab]

Merged — thank you!