Bug in jitterentropy handling

[Eric Berry]

Please see the attached patch.

The flag jent_rng_is_initialized is not being handled correctly.
- It is set to true before the corresponding jent_rng_collector structure
is fully initialized.
- It is not cleared when the jent_rng_collector is freed.

Subsequently, when trying to generate entropy in the function
_gcry_rndjent_poll after the jent_rng_collector has been freed,
jent_rng_is_initialized is true so jent_rng_collector is not
re-initialized, but then when trying to generate entropy jent_rng_collector
is null so entropy generation is skipped.

In Ubuntu, we want to create a userspace FIPS mode that generates entropy
solely through the jitter entropy library. Because of this bug, the
modifications we made to rndgetentropy.c to get all of the entropy from
_gcry_rndjent_poll goes into an infinite loop because _gcry_rndjent_poll
generates 0 random entropy. Consequently I think the existing code that
tries to generate 50% of the bytes from jitterentropy is actually getting
none.

This patch was generated against the master branch.
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