Replace some check_key in keygen tests with equivalent encoding
Replace some check_key in keygen tests with equivalent encoding

We really are wanted to check that a load+restore results in the same actual
key. Calling check_key over and over again is pretty expensive in the keygen
tests, and isn't really even the test that we want to perform.

randombit/botan,randombit/botan,randombit/botan,randombit/botan,randombit/botan