Didn't initialize the random wallet quite right.

First, the long_to_hex call was wrong - it put 192 Bytes of zeros before
the 64 byte random key. I fixed this to only use the randomly generated
part.

Second, on the advice of @cyc I am using random.SystemRandom() instead
of just random. The reason is right there in the python docs:

http://docs.python.org/2/library/random.html:
"The pseudo-random generators of this module should not be used for
security purposes. Use os.urandom() or SystemRandom if you require a
cryptographically secure pseudo-random number generator."

#yolocrypto

Thanks @cyc for the suggestion (see https://github.com/sbuss/bitmerchant/commit/d99661aaf0e3865c5d18753ec665a43f1b8602ab#commitcomment-5493500)