ANDROID: fips140: add dump_jitterentropy command to fips140_lab_util

For the entropy analysis, we must provide some output from the Jitter
RNG: a large amount of output from one instance, and a smaller amount of
output from each of a certain number of instances.

The original plan was to use a build of the userspace jitterentropy
library that matches the kernel's jitterentropy_rng as closely as
possible.  However, it's now being requested that the output be gotten
from the kernel instead.

Now that fips140_lab_util depends on AF_ALG anyway, it's straightforward
to dump output from jitterentropy_rng instances using AF_ALG.
Therefore, add a command dump_jitterentropy which supports this.

Bug: 188620248
Change-Id: I78eb26250e88f2fc28fc44aa201acbe5b84df8bb
Signed-off-by: Eric Biggers <ebiggers@google.com>
(cherry picked from commit dc015032)