Free memory properly for keygen and generate key everytime

Free memory properly for keygen and generate key everytime

[Title] Free memory properly for keygen and generate key everytime
[Issue#] P130426-7863
[Problem] Browser closed when using keygen twice
[Cause] Free already freed memory
[Solution] EVP_PKEY_assign_RSA(EVP_PKEY *pkey, RSA *key) uses the supplied key internally so key will be freed when the parent pkey is freed.
So do not free RSA if RSA is successfully assigned to PKEY.
Additionally, remove unnecessary RSA_new() for avoiding memory leak.
Also make keygen generate key for every submit press as it is the same behavior of other browsers.

Change-Id: Ie146c3c78698a0dd65190424afa7f861be5a08ac