Keystore 2.0 certificate utils: Set time by string.

Set notBefore and notAfter times using strings rather then architecture
dependent time_t.

Bug: 185119443
Test: atest keystore2_crypto_test
Merged-In: I83e64829b20d965f800e648d9b5d1452c526cb35
Change-Id: I83e64829b20d965f800e648d9b5d1452c526cb35
3 files changed