strongswan: Disable rdrand plugin.

Disabled because of security concerns.
httpscert: Use regular random source.

Previous to this patch, the kernel image file and internal
configuration settings have been used as a source for random
data, which is not random at all.
httpscert: Increase size of the RSA key to 4096.

RSA keys with length of 1024 bits are considered weak.
core74: Add httpscert script.