[Camel] Disable SSL v2 and weak ciphers by default

The change for disabled weak ciphers require at least NSS 3.14, thus
weak ciphers are enabled, if it's compiled with older NSS. In case
any server will require either weak ciphers or SSL v2 (while there
really should not anyone use it these days), then two environment
variables were added:

   CAMEL_SSL_V2_ENABLE=1 - to have SSL v2 enabled, otherwise it's disabled,
       regardless what camel providers request (they usually request v2 and
       v3 together)

   CAMEL_SSL_WEAK_CIPHERS=1 - to enable weak ciphers, almost the same as
       before; otherwise these are disabled and only those covered by
       NSS_SetDomesticPolicy() are enabled

These are added to the group of one for SSL V2 compatible hello:

   CAMEL_SSL_V2_HELLO=1 - to force SSL v2 compatible hello on SSL connections