Converts sstate so that it can use a hash equivalence server to
determine if a task really needs to be rebuilt, or if it can be restored
from a different (equivalent) sstate object.
The unique hashes are cached persistently using persist_data. This has
a number of advantages:
1) Unique hashes can be cached between invocations of bitbake to
prevent needing to contact the server every time (which is slow)
2) The value of each tasks unique hash can easily be synchronized
between different threads, which will be useful if bitbake is
updated to do on the fly task re-hashing.
[YOCTO #13030]
Signed-off-by: Joshua Watt <JPEWhacker@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
